Jarrod Mullen's NRL career hangs in the balance after the Newcastle star was provisionally suspended by the NRL for testing positive to an anabolic steroid.
The Knights and NRL announced today that Mullen had returned a positive sample to Drostanolone in an out-of-season test in late November.
The test came just a week after the 29-year-old aggravated a recurring right hamstring injury. Under the NRL's drugs policy, Mullen is facing a maximum four-year ban but can decide to have his B-sample analysed by the Australian Sports Anti-Doping Authority.
"The club is obviously extremely disappointed," CEO Matt Gidley said in a statement.
"The club has a strict governance program, the players are regularly educated and fully aware of the consequences of going outside our governance guidelines.