The Eels have fined forward Shaun Lane $17,500 over images that surfaced last week.
The fine comes after the NRL launched an investigation into an image of Lane holding a plastic bag with a white substance during what is believed to be the Sea Eagles' Mad Monday celebrations last year.
NRL.com understands Lane denied being in possession or consuming an illegal substance, although the club said on Saturday he had accepted responsibility and demonstrated genuine remorse for his actions.
"The Club is working closely with him to ensure he has a clear understanding of the Club's professional standards," the Eels said in a statement.