Mam is facing an NRL integrity unit investigation over Friday night's accident in the Brisbane suburb of Bardon, after he was detained by police and taken to hospital for further tests.
The 21-year-old had scans on his head in hospital after suffering a bump in the accident, but was later released and the injury is not believed to be serious.
Injuries to the occupants of the other car are also said to be not serious.
But Mam's head bump may only be the start of the five-eighth's woes.
The Broncos star underwent initial roadside drug and alcohol tests, to which he allegedly returned a positive result for drugs.
He was then ordered to undertake a second drug test using blood samples, with police awaiting the results of those.
Mam has not yet been charged.
"The man was subject to a roadside drug test where he allegedly returned a positive result," Queensland Police said in a statement.
"He was detained for further testing requiring bloods to be taken at hospital.
"Following this the sample is sent for analysis. This testing can take a number of weeks.
"The testing is conducted independently of the QPS (Queensland Police Service). The QPS cannot comment further whilst we await results.
"It will be alleged the 21-year-old man was unlicensed at the time of the incident."
Ezra Mam celebrates a try with Brisbane teammates against the Dragons. (Jono Searle/AAP PHOTOS)
The Broncos informed the NRL's integrity unit immediately on Friday night, after their welfare officers attended the scene of the crash.
It is the second drama to beset Mam since the end of Brisbane's horror season, after the NRL looked into an interaction between he, Reece Walsh and a fan in Bali last month.
It has already been a turbulent off-season for the Broncos, who split with coach Kevin Walters last month after their collapse from the 2023 grand final to 12th this year.
Michael Maguire has since been appointed as the club's new coach, and could have done without the latest issue.
Roadside drug tests have also become a constant issue for the NRL this season.
Cronulla playmaker Braydon Trindall tested positive to driving with drugs and alcohol in his system in May, and missed five games.
Canterbury flyer Josh Addo-Carr also missed the Bulldogs' elimination-final loss to Manly because of a positive roadside drug test.
Addo-Carr remains on the outer at Belmore following the test, and is expected to be released by the club with an NRL-imposed suspension still hanging over his head.
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