Manchester City face losing Kolo Toure for at least the rest of the season after the defender failed a drugs test and was suspended indefinitely from all levels of football.
City and the FA confirmed on Thursday that the 'A' sample provided by Toure had tested positive for a “specified substance” and he will not be able to play again until the disciplinary process has been resolved.
It is understood Toure believes he took a dietary aid unaware that it contained the illegal substance.
But FA rules state that lack of intent is not a valid defence.
Toure will definitely miss Saturday's match against Wigan and could theoretically be suspended for as long as two years.
The length of the ban will depend on the Ivorian's explanation as to how the substance found its way into his body, but Toure is expected to be sidelined for a number of months and is unlikely to feature again this season, with bans typically ranging from three to nine months.
The 29-year-old, who signed from Arsenal in July 2009, was informed of the positive results hours before City's FA Cup fifth round tie against Aston Villa on Wednesday night and was withdrawn from the squad.
“Manchester City confirm that the FA has informed Kolo Toure that an ‘A-sample’ provided by him has tested positive for a specified substance,” said a statement on the club's official website on Thursday.
“As result of this, he has been suspended from participating in all first team and non-first team matches pending the outcome of the legal process.”
The World Anti-Doping Agency defines “specified substances” as those “more susceptible to a credible, non-doping explanation”.
It is unlikely, then, that Toure has tested positive for a recreational drug.
Nevertheless, WADA's code states the punishment can range from a warning to a two-year ban.
It states: “If the athlete can prove that he or she did not intend to enhance performance by using them to the satisfaction of the results management authority, the sanction under the World Anti-Doping code can go from a warning to a two-year ban.”
Former Sheffield United goalkeeper Paddy Kenny was banned for nine months in September 2009 after he tested positive for ephedrine, a stimulant found in cold cures.
In January Hamilton's Simon Mensing was suspended for four weeks after failing a drugs test for methylhexaneamine, a substance contained in a dietary supplement.
Toure, who cost £14m two summers' ago, was City's captain last season and is now vice-captain at Eastlands behind Carlos Tevez.
Signed by Mark Hughes after seven years at Arsenal, he is regarded by his team-mates as a model professional and, as a devout Muslim, does not even drink alcohol.
His expected absence will come as a blow to City manager Roberto Mancini as Toure has built a strong partnership with Vincent Kompany this season.
City are still challenging for the FA Cup and Europa League, while the priority remains a top-four finish in the Premier League.