Sale Sharks prop Karena Wihongi has been suspended from playing for four months after testing positive for banned stimulant methylhexaneamine.
The 31-year-old was provisionally suspended by the Rugby Football Union on 28 January for failing a drugs test after Sale's game with Newcastle.
He then appeared before a disciplinary panel and it was ruled he would not be allowed to play again until 27 May.
The club have confirmed they will not be appealing against the decision.
A statement on the Sale website says the club and player told the RFU panel that the stimulant entered Wihongi's body "without his knowledge and without any pre-meditated plan to gain an advantage".
It continued: "It was demonstrated to the panel that the stimulant became present via a contaminated product that was available through the club's supplements programme.
"When the product in question was supplied to the club it was issued with a batch test certificate that showed no traces of any banned substance. The ingredients of the product had previously been checked and all had been cleared.
"Sale Sharks would like to place on record our full support for the UK Anti-Doping Testing Programme. There is no place in sport for drug cheats and the penalties enforced for those that attempt to gain an advantage by using banned substances are correct and appropriate.
"However the club are frustrated and disappointed with the verdict given to a player who without his knowledge took a product that was wrongly contaminated."
Former Oyonnax front-rower Wihongi, who was born in New Zealand but is qualified to play for France on residential grounds, joined the Premiership side last summer from Bourgoin on a two-year deal.
He made his debut on the opening day of the season against Newcastle and went on to make 10 appearances before failing the drugs test after the reverse fixture against Falcons on 7 January.
Under the terms of his ban, which runs from the date of his provisional suspension, Wihongi is not able to participate in playing, training, coaching, officiating, selection, team management, administration or promotion of the game.
Commenting on Wihongi's suspension, Rugby Players' Association chief executive Damian Hopley says there is an inconsistency of punishments handed out to players: "The RPA fully endorses the fight against doping in all forms of sport and actively promotes strong anti-doping messages to all of our members.
"But we are extremely concerned at the inconsistency concerning the recent punishments handed out to players who have unknowingly taken these contaminated substances containing the stimulant methylhexaneamine.
"The fact that Karena was given the supplement at half-time in a game with the tacit understanding that the substances were certified as clean, seems to have had no impact whatsoever in the sentence that was subsequently passed.
"While we fully accept that all athletes are ultimately responsible for whatever supplements they ingest, the RPA will be taking up this matter with the relevant national and international authorities as we believe this inconsistency and the lack of empathy shown in this case is wholly unacceptable in professional sport."