Chelsea boss Jose Mourinho has said he is unsure whether the transfer of Benfica midfielder Tiago will go ahead.
The Portuguese international was at Stamford Bridge on Tuesday to discuss personal terms after passing a medical, but the deal has hit a stumbling block.
Chelsea and Benfica are thought to have agreed a fee of about £10m for Tiago.
But Mourinho said: "He is still a Benfica player. I understood some negotiations were made, but I am not sure about the end of them."
Earlier on Tuesday, chief executive Peter Kenyon was confident Chelsea would get their man, and also tie up a deal for Marseille striker Didier Drogba.
He said: "Tiago and Drogba are both at Stamford Bridge now and we are hoping to complete those deals later today.
"They are both progressing well."
But it seems that while the deal for Drogba, according to Mourinho, is "99.5%" certain, Tiago's transfer could be in the balance.
Tiago, 23, is under contract with Benfica until 2007 but is keen to leave because of differences with the club's new chief Jose Veiga.
"I would not feel good if I stayed at Benfica," Tiago told Portuguese newspaper A Bola.
"If everything goes well, my present and future will be at Chelsea."
Mourinho has insisted any new signings must be completed by Wednesday, when the squad leave for a tour of the United States.
If the deal for Tiago collapses, it could open the door for Juventus, who were interested in signing the midfielder in the aftermath of Euro 2004.
It would be ironic if Juve did pip Chelsea to the Portuguese star, after the Blues outbid the Serie A club for Drogba.