Castleford player Zak Hardaker has apologised for making "an enormous error of judgement" after failing a drugs test, in a statement on the Super League club's website.
The full-back has been provisionally suspended for testing positive for a "banned substance" and will not be included in England's squad for the World Cup.
He added: "Finally, I would like to make it clear that in no way did I, nor would I, ever take a substance with the intention of enhancing my performance."
A Rugby Football League Spokesperson said:
Hardaker was dropped by Castleford for Saturday's Grand Final against his former club Leeds for what the Tigers said was a breach of club rules.
However, Castleford captain Michael Shenton refused to blame the absence of Zak Hardaker for his team's worst performance of the season as they crashed to a 24-6 defeat to Leeds in their maiden Grand Final.