West Ham United face the threat of being thrown out of the FA Cup after Fifa announced that it was taking disciplinary action for a "potential violation" of rules over Diafra Sakho's participation in the 1-0 victory against Bristol City.
In a development that could have huge ramifications for the FA Cup this year, Fifa is investigating Sene-gal's complaint after Sakho played - and scored the winner - in West Ham's fourth-round match despite being unavailable for the Africa Cup of Nations.
Sakho did not travel to Equatorial Guinea for the tournament due to a back injury that, according to West Ham, prevented the striker from -flying. Unless there is prior -agreement with the national association, Fifa rules state that players cannot appear for their clubs during the period they should have been released.
The disciplinary measure for any proven violation is stated in paragraph 6.2 in the annexe of the Fifa regulations on the status and transfer of players. It reads: "If a club refuses to release a player or neglects to do so despite the provisions of this annexe, the Fifa Players' Status Committee shall furthermore request the association to which the club belongs to declare any match(es) in which the player took part to have been lost by the club concerned.
"Any match contested according to the cup system shall be regarded as having been won by the opposing team, irrespective of the score."
West Ham are adamant that they have not broken the rules and have already called for the proceedings to be dropped. Fifa has offered no time-scale for their investigation, despite there being only 10 days until West Ham are due to play their fifth-round tie against West Bromwich Albion.
It is unclear how the Football Association would respond to any Fifa demand for West Ham's fourth-round win to be overturned, particularly if it was not made until after further matches in the competition have been played. The FA is well aware of Fifa's rules and would take its own legal advice for what would be an unprecedented situation.
Bristol City are also monitoring Fifa's investigation and, if it was proved that Sakho should not have played against them, they appear more likely to seek financial redress rather than reinstatement into the competition. They would have won pounds 90,000 in prize money for reaching the fifth round but there would also have been income from gate receipts and the possibility of progressing even further.
West Ham have released a bullish statement. "Diafra Sakho and West Ham United vigorously deny that they have acted in breach of Fifa regulations," the club said. "They regard the proceedings as clearly unfounded and are requesting their dismissal."
West Ham are adamant that Sakho did not join Senegal because of a back problem that meant he could not fly. It is understood that they have already supplied a medical report to Senegal, carried out by a specialist, stating this. Sakho was then only cleared to play in the Bristol game if he did not fly with the rest of the squad and travelled by car.
West Ham, though, did pull Sakho out of the Premier League match against Liverpool on Saturday after hearing of Fifa's investigation.
No decision has been taken on whether Sakho will play against Man-chester United on Sunday, although Senegal are now out of the Africa Cup of Nations.
There are a series of Fifa regulations and "principles" about the protocol that should have been followed. The starting point is that "clubs are obliged to release their registered players to the representative teams" of their country if they are called up.
They also say that the national associations must notify the player and club in writing at least 15 days before the 14-day preparation period for a tournament. If a player cannot comply because of injury, the national association, in this case Senegal, can then have their own doctor perform a medical examination.
West Ham are not aware of Senegal taking up the option to check Sakho's back injury in England after he was made unavailable.
The guidelines, however, also state that a player is "not entitled to play for the club with which he is registered during the period for which he has been released or should have been released pursuant to the provisions of this annexe."
This is subject to there being any agreement with the national association. Legal interpretations of these particular clauses are likely to be mixed but would appear crucial to the outcome of the case.
Fifa is now seeking all the respective communications between Sakho, West Ham and Senegal.
A Fifa statement said: "We can confirm that disciplinary proceedings were initiated against the player
Diafra Sakho and the club West Ham United for a potential violation of the Fifa Regulations on the Status and Transfer of Players."