Manchester City defender Kolo Toure has been suspended from playing after testing positive for a "specified substance" in a recent drug test.
The Ivorian defender was informed by the Football Association that his A sample returned a positive result and he is now unavailable to take part in any matches until the issue has been investigated.
The World Anti-Doping Agency define a specified substance as one that is "more susceptible to a credible, non-doping explanation".
The WADA punishment for such a positive test ranges from a warning to a two-year ban.
Hamilton midfielder Simon Mensing recently served a four-week ban after he tested positive for a specified substance.
The 28-year-old tested positive for the stimulant methylhexaneamine at the end of January and subsequently missed five matches after a period of ineligibility was imposed on him.
The player maintained he was unaware he had ingested the substance while using a dietary supplement - an explanation which was accepted by UK Anti-Doping.
It is understood that Toure was not included in City's squad for Wednesday night's FA Cup match against Aston Villa because the club were aware of the situation.
The failed test automatically triggered the suspension, with City left with no option but to exclude him from their plans until the conclusion of proceedings.
Announcing the news in a short statement on the club website, Manchester City said: "He has been suspended from participating in all first team and non-first team matches pending the outcome of the legal process.
"There will be no further comment from the football club at this stage."
The FA verified a suspension was currently in place, adding: "The FA can confirm that a player has been provisionally suspended from playing pending investigation, having tested positive for the use of a prohibited substance."
The 29-year-old centre-back joined City for £14million in 2009, ending a seven-year association with Arsenal.
Gunners boss Arsene Wenger had signed him from Ivorian side Mimosas and he went on to captain the club on a number of occasions before heading to Eastlands, where he served as club captain under Mark Hughes until he was succeeded by Carlos Tevez for this season.