Scotland are not fielding a second string XV against South Africa, insists Jonathan Humphreys as Dark Blues train at St James' Park ahead of Rugby World Cup clash

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Scotland assistant coach Jonathan Humphreys insists Scotland are not gambling with their World Cup ambitions after rejecting claims they are putting out a second string line-up against South Africa.

The Dark Blues can all but clinch a quarter-final slot if they become the second Pool B team to beat the Springboks when they clash at Newcastle's St James' Park.

But Vern Cotter has again tinkered with his team ahead of facing Heyneke Meyer's men, making a raft of changes.

The Scotland squad train at Newcastle United's St James' Park ahead of their clash with South Africa

Vern Cotter's men huddle as they prepare for Saturday's crucial World Cup match against the Springboks 

Scotland's Josh Strauss (centre) collects a pass during Friday's training session in Newcastle 

Al Dickinson, Ross Ford, Mark Bennett and Sean Maitland, key performers for the Scots in their opening two victories over Japan and the United States, are either benched or rested altogether.

Cotter is also without injured duo Finn Russell and John Hardie and in all, seven members of the starting XV to face the two-time former winners are not regarded as the Kiwi's first picks.

But Humphreys denies the head coach has written off beating the Boks in preference to keeping his men fresh for their final - and potentially decisive - group game with Samoa.

He said: 'I don't understand why people are saying it's a second string. What hasn't been written is that international rugby is a hugely, hugely physical sport.

'I'd prefer them to write about a 31-man squad playing three huge games in 10 days.

'We're confident in the group we've picked. Look at the two Gray brothers [Richie and Jonny]. We have a fantastic back row. Blair Cowan played every single game in the Six Nations and was extremely unlucky not to get in the initial 31-man squad.

Blair Cowan stretches during Friday's session after being called up to the squad to replace Grant Gilchrist

Captain Greig Laidlaw will start Saturday's match with South Africa as Scotland look to reach the quarter-finals

Scotland's team to face Rugby World Cup Pool B rivals South Africa on Saturday afternoon

'We have Gordon Reid who played extremely well against France. There is Fraser Brown, who's arguably been our best forward in this tournament so far. He's been outstanding.

'They're an extremely proud group of people. I haven't seen a more together group. We are all after the same thing - every single player has worked so hard to be here and they're here on merit.

'Next week will be next week. Our sole focus is on this game, and we cannot take our focus off this game.

'Right now we've not thought about Samoa. South Africa are an unbelievable threat to us and we want to get the job done.'

Centre Bennett scored twice in Scotland's first match against Japan but his place is taken by 6ft 5in former flanker Richie Vernon.

Matt Scott (left) uses an advertising hoarding for balance as Scotland's players go through a warm-up

Scotland head coach Vern Cotter, pictured exiting the tunnel at St James' Park, has made a raft of changes

Saturday's match will be just the Glasgow man's third international start at 13 since converting from the back row but his midfield partner for the afternoon Matt Scott denies he is going up against one of the world's strongest outfits with a rookie by his side.

'Richie hasn't played centre for long but I've found him to be a really easy guy to work with,' said the Edinburgh back. 'He's a quick learner, so he takes on information easily. I've no real issues with him.

'He's not [an additional burden on me] at all. He's played in the back row so he's a very good tackler. I don't see it as a weakness for us. We have two physical guys just like they do, so we're well matched in the midfield.'

Scotland have struggled to deal with the driving maul and they now take on a side who have got the technique down to a fine art.

'That's the game right there - the line-out and the mauls,' admitted Scott. 'The forwards are going to have an extremely tough day.

Glasgow Warriors star Tim Swinson goes for a run as Vern Cotter's players are put through their paces

'As a backline we just have to help them out as much as we can. That means making our tackles and putting them back when we get the chance because we know it's going to be tough for them up front.'

Meyer claimed earlier this week his side had been forced to change their line-out calls as they feared Afrikaners-turned-Scots Josh Strauss and WP Nel would be able to crack their codes.

Both players trained with South Africa before committing themselves to Scotland but Humphreys, now in charge of the forwards, said: 'I don't think it's possible to change a complete book of line-outs in a week.

'Their line-out is very effective and simple. Whether they change, I don't know. It's not something we've even talked about.

'Are they at it? I don't know. I don't think it's quite as monumental as they've made out.'