- Timeline: How the Crowley case unfolded
- Crowley facing ban after positive test to banned substance

RYAN Crowley most likely took a narcotic-based painkiller, leading sports doctor Peter Larkins suspects.

When Larkins spoke with AFL.com.au on Monday afternoon he was at pains to say he had no inside knowledge of Crowley's positive match-day test that had led the Dockers tagger to accept a provisional suspension while he awaits an AFL Anti-Doping Tribunal hearing.

Athletes found guilty of taking narcotic-based substances face a ban of up to two years under the World Anti-Doping Agency and Australian Sports Anti-Doping Authority codes.

Fremantle CEO Steve Rosich said on Monday that Crowley had taken a painkiller that had not been prescribed to him by the club's medical staff.

Larkins said this suggested to him that Crowley had probably taken a narcotic-based substance.

"There are only a small choice of painkiller tablets that can be used on match day," Larkins said.

"With pain killers on match day you are allowed to use Panadol and aspirin but not anything that has a narcotic component.

"When you're dealing with reasonable pain in everyday life, narcotic-based painkillers are used pretty commonly. Every day doctors would be prescribing a pain-relief tablet for high-strength pain and anyone who leaves hospital after a shoulder reconstruction or a knee reconstruction could be on such medication for a week.

"They are not performance-enhancing drugs but they're banned on the basis that if you're trying to mask pain to play sport the WADA rules have said that it's not healthy to mask pain of that severity.

"If you've got a broken ankle and I'm prescribing you a narcotic-based painkiller so you can run around the footy field, the ASADA code would say that's bad for your health and therefore it's banned for me as a doctor and you as a player to use that sort of painkiller."

Larkins said it was also possible Crowley had taken a tablet with a codeine compound.

Although typically used as a cough suppressant, codeine is also a narcotic-based painkiller, he said.

Larkins said in his experience it was extremely unusual for a player to seek prescribed pain relief from outside his club's medical staff.

The sports medico said the fact that ignorance is no excuse under ASADA rules meant players who took substances that had not been cleared by their club doctors were taking a big risk.

"This is really drilled into all of the footballers when they have their drug talk each year from the AFL so it's a pretty basic mistake to make," Larkins said.

"Their club doctors have a list of the stuff that's acceptable and they're available to hand out pain relief to players every day at the club.

"So it's not as if they can't get something from their club supplies."