Michael Jennings, who has played for both Australia and Tonga, was provisionally suspended after returning a positive A-sample for Ligandrol and Ibutamoren, both prohibited by the World Anti-Doping Agency.
The NRL said the Parramatta Eels player was tested on September 21 with the results coming through on Friday.
Reports said he was door-knocked by Sport Integrity Australia agents at his home early Saturday, and his mobile phone and computer were seized.
“Mr. Jennings is prohibited from participating in any WADA compliant sport, including rugby league, while the provisional suspension is in place,” the NRL added in a statement.
It ruled him out of Saturday’s elimination final between the Eels and South Sydney.
Under the sport’s anti-doping policy, the 32-year-old, who is yet to comment publicly, has the option to have a B-sample analysed.
His club Parramatta said it was in contact with Jennings and “will continue to offer him and his family our full wellbeing support”.
Ibutamoren is a growth hormone while Ligandrol, an anabolic agent, helps build muscle. Australian relay world-record holder Shayna Jack also tested positive for Ligandrol ahead of last year’s world swimming championships.
Meanwhile, police arrested St George Illawarra’s Tristan Sailor, 22, at his home south of Sydney on Saturday and charged him with aggravated sexual assault.
He is the son of Wendell Sailor, who played both rugby league and union for Australia.
He is accused of attacking a woman at a home in Sydney last week, a New South Wales police statement said.
Sailor was once rated one of the sport’s most promising prospects but managed only five games for the Dragons since his debut last year, and was recently told his contract would not be renewed.
“The club is taking the matter very seriously and will continue to work with Tristan and all relevant authorities,” the Dragons said.
He was refused bail and is due to appear in court on Sunday.