Manchester United goalkeeper Fabien Barthez is in talks with Marseille with a view to joining the French side on loan.
Barthez has lost his first-team place
But both clubs have been warned by the football authorities that the move would have to receive special dispensation because it would be taking place outside the transfer window.
"The matter must go before Fifa's players' status committee after the French FA have submitted the necessary paper-work," said Fifa president Sepp Blatter.
Marseille said on their website they expected to complete Barthez's move from the English champions by the end of the week, but that now looks unlikely.
While United confirmed that negotiations were underway, a spokeswoman said: "No agreement has been reached."
Old Trafford boss Sir Alex Ferguson has revealed he is letting the 1998 World Cup winner go because his chances of first-team football are limited.
Barthez has also been warned he faces losing his place as France's number one unless he gets senior football.
Barthez, who signed from Monaco for £7.8m in May 2000, has found himself as third-choice at Old Trafford, behind summer signing Tim Howard and Northern Ireland's Roy Carroll.
The 32-year-old played for Marseille until 1995, winning the European Cup with them in 1993.
Ferguson said: "There is nothing worse for me than seeing a player of that calibre not getting a game of football - he's a good lad and hopefully this will help him.
"He's going to speak to Marseille. They approached us and there are one or two things to be ironed out.
"The reason I'm happy to let the move go through is that it leaves me with two experienced keepers in Tim Howard and Roy Carroll.
"In fairness to Fabien, the longer he's going to be here without getting a game there is going to be a problem for him.
"He's a terrific goalkeeper, one of the best in the world, but just by opportunity Tim Howard has taken the number one jersey.
"When we signed Tim we did think he was going to challenge for the position - we didn't think he was going to be as good as he has been. He has been absolutely outstanding."
Marseille president Christophe Bouchet is convinced that the swap will be confirmed by the weekend.
He announced the news on the club's website, and is awaiting Fifa ratification because the proposed loan is taking place outside the allotted transfer window.