By Jonathan Stevenson and Caroline Cheese

When Thierry Henry completed his £16.1m move from Arsenal to Barcelona in June 2007, football purists could barely contain their excitement.

One of the most extravagantly gifted players of his generation was joining a club that already boasted three such talents in Ronaldinho, Samuel Eto'o and Lionel Messi.

'The Four Fantasticos' were meant to produce football from a different planet. But 30-year-old Henry, in particular, has come crashing back down to earth after a season of immense frustration.

606: DEBATE Give us your thoughts on Thierry Henry's struggles

The man who lit up the Premier League for so long is a shadow of his former self as Barca, ravaged by injuries, torn apart by in-fighting and cast as underdogs, prepare to face Manchester United in the semi-finals of the Champions League.

With doubts now circulating as to whether he will even start the first leg on Wednesday, BBC Sport looks at just what has happened to Thierry Henry.

Does the Thierry Henry who played with such devastating speed and skill at Arsenal still exist?

After enjoying seven seasons as a Gunner with hardly any injury problems, Henry's final year in England was blighted by foot, back, stomach and groin injuries and a sciatic nerve problem that ended his campaign in March.

WHAT THE SPANISH PRESS SAY Another world champion for Barca - the most brilliant and effective striker on the continent Barca daily Sport, 23 June 2007

Henry admitted in October 2007 that he would have liked more time to build up his fitness.

"It would have been better to go into the team step by step but then Eto'o got injured and other players were not ready after the Copa America," he said.

"I had to come back to fitness and play at the same time."

Spanish football expert Graham Hunter believes Henry was unfortunate that he joined Barcelona at such a problematic time in his career.

"At that stage he was a broken athlete and he came to Barcelona to try to rehabilitate himself physically," he told BBC Sport.

"There are rumours he failed his medical but I don't put faith in that because actually the club and Thierry have been quite forthcoming about it, that his medical was partial because he had been out for so long at the time he had to sign."

THIERRY HENRY FACTFILE Born: Les Ulis, Essone, Paris on 17 August 1977 Clubs represented: AS Monaco (1994-99), Juventus (1999, cost £10.7m), Arsenal (1999-2007, cost £10.5m), Barcelona (2007- , cost £16.1m) International career: 98 caps, a French record 44 goals Did you know: Wears the number 14 shirt at Barca, once worn by the great Johan Cruyff

The main cause of Henry's recent injury troubles is a near-chronic back problem, officially diagnosed as the dehydration of an intervertebral disc, which causes lumbar and hip pain.

Former vice-president Sandro Rosell has gone as far as to say that the club made a huge mistake in signing Henry.

"Whoever signed him deserves a clip round the ear," stated Rosell in December. "He should have been given an exhaustive medical."

But Barca coach Frank Rijkaard, clinging on to his job in the face of fierce criticism from the media and fans as his side have slipped way behind Real Madrid in La Liga, defiantly believes Henry will return to his very best.

"Thierry has suffered with the aftermath of an injury and for so long that has stopped him from performing optimally," said Rijkaard earlier this month.

"But he's had his value in many games. He hasn't quite been the player we imagined when we bought him but he is a player who I still think can become that."

Henry's move to Spain came at a difficult time in his personal life as he was going through a divorce with his English wife Claire at the time.

She stayed in London with his two-year-old daughter Tea and Henry recently admitted he has found it hard being away from his only child.

Henry has freely admitted how much he has missed daughter Tea

"My daughter is the most important thing in my life," said Henry on 13 March. "I'm not happy because a father who sees his daughter five times in eight months cannot be."

According to Hunter, the Barcelona fans think Henry's public admission that he is missing his daughter could mean he is on his way at the end of the season.

"They are pretty pragmatic people, the Catalans," he added. "They expect that if he's missing his daughter as much as he says he is, they think this might be his only season at Barcelona."

Rijkaard has conceded that Henry's personal situation has been a "difficult thing" for the Frenchman.

But one thing Henry has not struggled with is the language - after only 10 months in Spain, he is already speaking fluently in news conferences.

Barcelona, from their youth teams up to their senior side, steadfastly play a 4-3-3 formation. This is partly the result of the influence of former coach Johan Cruyff, a man who put in place the Barca youth academy structure that has produced so many outstanding talents.

Thierry Henry: "I've never run as much in all my career"

When Rijkaard's Barcelona were at their best, he had Ronaldinho down the left, Eto'o through the middle and first Ludovic Giuly and then Messi down the right.

The three were interchangeable and the fluidity of the frontline produced some devastating results.

When Barca bought Henry last summer, the club thought it had a player who could easily slot into any of the front three positions.

But after he was heavily criticised for an ineffective display in the Champions League quarter-final, second leg win against Schalke, Henry aired his frustrations at his new position.

"I have never run as much in all my career. Never, never, never, never, never," he revealed.

"Instead of running off the shoulder of defenders 30 metres from goal, I'm going from 60! As far as beating the last man is concerned, forget it, my legs are gone by then."

Hunter believes Henry has become a victim of poor planning by the Catalan giants.

"In footballing terms, the board dominated over the coach. They just wanted Henry to adapt, irrespective of whether he wanted that or was able to do that.

WHAT THE SPANISH PRESS SAY Until the 49th minute, if someone had said Henry was actually in London, you would have believed them La Vanguardia, 10 April 2007, after the 1-0 Champions League win over Schalke

"I think the planning for how to incorporate Henry into this squad was done in an immature way and actually is typical of how badly Barca have planned in the last 24 months.

"I spoke to one of the club's vice-presidents on the day he signed and once we had done our on-the-record chat, he spoke some more and just gurgled boyishly with excitement about the amount of money Barca were going to make from the Henry brand.

"I think the expectations were probably aimed more towards buying a brand than buying the type of footballer they needed."

Henry's plight is something former England striker Gary Lineker knows all about.

Lineker, who made a £2.2m move from Everton to Barcelona in 1986, was also forced to play out of position at the Nou Camp.

Crucially, though, he was already a hit with the fans when in his third season at the club, new manager Johan Cruyff shifted the striker on to the wing.

It was a move that prompted an unhappy Lineker to end his spell in Spain but he expects Henry to adapt given time.

"I'm a lot different to Henry. He is a much better player than I was," said the BBC sports presenter.

"But he was always the fulcrum of Arsenal's play. He's not at Barca. He used to be a winger when he was younger and it's not a difficult position compared to where he was playing but it's probably not giving him as much satisfaction or involvement."

Rijkaard, for his part, has dismissed the notion he forces Henry, who has played in the injured Ronaldinho's left-sided position for much of the season, to stay in an unfamiliar position out on the touchline.

"I always tell him before games not to feel restricted and I am never going to ask him to do the impossible," insisted the Dutchman.

So will Henry's season of frustration be his only one at Barca?

Lineker is adamant that Henry simply needs time but he admits that the pressure can be uniquely intense at the Nou Camp.

"They call it 'mes que un club', which means more than just a football club - and it is really.

WHAT THE SPANISH PRESS SAY There's no way of getting him to play well. Not even the Champions League could reactivate him El Mundo Deportivo

"It is a way of life, it is quite political and consequently they don't have a lot of patience with players.

"It makes the extremes of success and failure greater. When you are doing well you are the king and when you're not you are hopeless, even more so than in England."

But despite Barca's public statements that they will not sell Henry, Hunter believes the odds are stacked against France's all-time record goalscorer staying in Catalonia beyond the summer.

"Barcelona expected so, so much more from Thierry," he said.

"The press have been relentlessly disappointed in their match coverage and their interviews with him are often very tense, verging on the hostile.

"As for the fans, they waited a long time and were very patient but that patience has now run thin. Very many people think they won't ever now see the best of Henry."

Henry will come up against old foes in the Champions League

So with his future at Barcelona becoming more uncertain by the day, Henry will look to two matches against his old foe Manchester United to reignite his career and show he can get back to his best.

But Hunter says to expect a great performance from the former Monaco flier would be to expect too much.

"A great performance is beyond him. He's out of form, his touch is poor," stated Hunter.

"Sometimes, however, football throws up a story whereby luck, form, injury, exceptional performances from a Messi or an Eto'o might be complemented by Henry's nous, experience and the fact he knows about United as a football team.

"All of those things may combine to offer him a moment in the spotlight."

With the eyes of the world on him and the Barcelona fans ready to turn on their most recent scapegoat once more, Thierry Henry - now more than ever - needs to produce something special.

His career at the very highest level might just depend on it.