Newcastle Knights halfback Jarrod Mullen has tested positive to an anabolic steroid.
Traces of Drostanolone were found in a sample the halfback had provided in an out-of-season test in November, a week after the 29-year-old suffered a hamstring injury.
If charged, Mullen faces a maximum four-year suspension.
“The club is obviously extremely disappointed,” CEO Matt Gidley said. “The club has a strict governance program, the players are regularly educated and fully aware of the consequences of going outside our governance guidelines.
“From here, there is a formal process we need to follow under the guidelines. We need to respect the process and in the interim the club will continue to monitor Jarrod’s welfare.”