Mamadou Sakho has been suspended provisionally by UEFA for 30 days, after the Liverpool defender tested positive for drugs.
A sample submitted by the defender to the European football body tested positive for traces of banned substance, believed to be a fat burner.
Sakho had the option to appeal the finding and have a B sample tested, but it was revealed on Wednesday that he had declined to take this option.
UEFA has now elected to suspend the player for a month while an investigation is undertaken.
A release from European football’s governing body reads: “Disciplinary proceedings have been instigated against Liverpool FC player Mamadou Sakho, following the UEFA Europa League round of 16 second-leg match between Manchester United FC and Liverpool FC (1-1), played on 17 March.
“The proceedings relate to a violation of the UEFA Anti-Doping Regulations, after the player failed a doping test at the above-mentioned match.
“The player did not request the analysis of the B sample. UEFA has now suspended the player provisionally for 30 days until a final decision is taken by the UEFA Control, Ethics and Disciplinary Body.
“The date of the disciplinary hearing will be announced at a later stage.”
Team-mate Kolo Toure only received a six-month ban for admitting liability to using diet pills while at Manchester City in 2011, with an independent regulatory commission stating: “The player accepted he was at fault and with that concession we agree.
“He was at fault in the limited and perfunctory efforts he made in relation to the water tablets; the checks he made in relation to those tablets were inadequate and fell some way below what it would be reasonable to expect of a professional footballer in these circumstances.”