Parramatta star Michael Jennings has been provisionally suspended after testing positive to banned substances.
It means the gun centre will miss the Eels' do-or-die semi-final against South Sydney tonight.
The NRL released a statement confirming Jennings had tested positive to Ligandrol — the same substance banned Australian swimmer Shayna Jack is alleged to have ingested.
"The Provisional Suspension Notice asserts that Mr Jennings returned a positive A-sample for LGD-4033 (Ligandrol) and its metabolite Di-hydroxy-LGD-4033, and also Ibutamoren and its metabolites Desbenzyl Ibutamoren and OH Ibutamoren," the NRL statement said.
"Each of those substances are prohibited by the World Anti-Doping Agency (WADA) and the NRL's Anti-Doping Policy.
"Mr Jennings was tested by Sport Integrity Australia (SIA) on 21 September 2020 with the positive result received by SIA on 9 October 2020.
"Mr Jennings is prohibited from participating in any WADA compliant sport, including rugby league, while the provisional suspension is in place."
Parramatta released a statement in response to the bombshell, reiterating the NRL's point that Jennings can request to have his B-sample analysed.
"Michael Jennings has been stood down from today's game and ongoing training/playing responsibilities while the process runs its course, which under the policy includes the opportunity to have his B-sample analysed," the statement said.
"The club has been in contact with Michael and will continue to offer him and his family our full wellbeing support."
Jennings' suspension is a major blow to the Eels, whose premiership campaign had already been derailed by the losses of barnstorming winger Maika Sivo and fellow flanker Blake Ferguson.
Both of Parramatta's major metre-eaters have been ruled out with injury and coach Brad Arthur will need to make more changes now the backline has been decimated even further.
NRL reporter Brad Walter said on Twitter Jennings' ban was a "massive shock and disappointing news", while AAP's Scott Bailey wrote: "Hard to believe what has transpired this morning. Michael Jennings is such an important figure at the Eels. His brother George is still left to play tonight, while he's been a big influence on Waqa Blake in the past week alone. Disasters don't get much bigger than this."
Nine's Danny Weidler added: "The Michael Jennings news is so disappointing."
Broncos legend Darren Lockyer told Nine's Today Show the drama will "no doubt" be a distraction for Jennings' teammates tonight.
The Eels were torn apart on the edges by Melbourne last week, prompting Jennings to turn coach at training, conducting one-on-one video sessions with teammate Waqa Blake about his decision-making in an effort to ensure Parramatta can hold out Souths tonight.
But losing one of the team's most experienced players just made that task a whole lot tougher.
Jennings has played nearly 300 NRL games after making his first grade debut at Penrith in 2007 before a stint with the Roosters was followed by his move to Parramatta in 2016.
He was a NSW Origin mainstay during the middle of his career, representing the Blues 18 times. The 32-year-old has also won seven caps for the Kangaroos.