The Newcastle Knights has been made aware the NRL has provisionally suspended Jarrod Mullen under the NRL's Anti-Doping Policy.
The Provisional Suspension Notice asserts that Mullen returned a positive A-sample for an anabolic steroid, Drostanolone which is prohibited by the World Anti-Doping Agency (WADA) and the NRL's Anti-Doping Policy.
He was tested by the Australian Sports Anti-Doping Authority (ASADA) on November 29, 2016.
Mullen is prohibited from participating in any WADA compliant sport, including Rugby League, while the provisional suspension is in place.
Under the Anti-Doping Policy, Mullen now has the opportunity to have his B-sample analysed.
"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."