Sam Allardyce admits there is a "slight door" still open for Emmanuel Eboue at Sunderland, despite the Black Cats terminating the defender's contract.
Sunderland today issued new signing Eboue with two weeks notice after a statement from FIFA which confirmed that the 32-year-old has been banned from all football activity for the next year.
Eboue - who only agreed a short-term contract at Sunderland earlier this month - has failed to settle a six-figure debt to his former agent Sebastien Boisseau after he was ordered to pay the sum at a FIFA hearing almost two years ago.
The ex-Arsenal defender never made Sunderland aware of the issue when he agreed a deal at the club, and the Black Cats had no other way of learning about the case from either the FA, Premier League or FIFA.
But the ban will be revoked if Eboue pays the outstanding debt, which could see him brought back into the fold at the Stadium of Light.
Sunderland boss Allardyce said: "I feel a little bit let-down by the situation because we didn't know anything about it and we couldn't intervene in the end.
"It was a straightforward case of getting it sorted or getting banned.
"He's tried to negotiate that, but not been able to and the ban has actually come through.
"He can't even come anywhere near the training ground, never mind a football match.
"There will still be a slight door open if he can resolve the situation in the next few days because we've spent a huge amount of time getting him fit ready for the first-team.
"We were looking forward to bringing him into the squad and hopefully forcing his way into the side based on his abilities at his former clubs.
"For us and him, it's a shame that we're in this situation, but it's not our fault. It was nothing we could have foreseen.
"The confidentiality clause means neither the FA or Premier League could have flagged it up for us."
After spending a month on trial at Sunderland, Eboue never made a competitive appearance for the club, but enjoyed one outing for the Under-21s, while he made his return from a hamstring injury in a behind-closed-doors friendly against Middlesbrough last week.
But after being released by Galatasary at the end of last season, Allardyce fears that the ban could spell the end of Eboue's career.
"He's put a huge amount of time into getting a contract until the end of the season," added Allardyce.
"If he doesn't get it sorted out, this is a huge problem for him.
"If he lets it linger on and on, is he ever going to play football ever again?
"It's a significant amount and he's tried to negotiate that, but the talks have broken down.
"Unfortunately it's been at Sunderland Football Club when it's come to a head and we suffer the consequences as well as him."