Fremantle forward Michael Johnson is under investigation from WA police after reportedly being found with a small amount of cocaine.

"WA Police are investigating a drug-related matter on the weekend involving a current AFL player, no charges have been laid at this stage and no further details are available for release," a police statement said.

"We will be making no further comment until the investigation has been concluded."

A Fremantle spokesman refused to confirm or deny Johnson had been caught with cocaine but the Dockers released a statement in which chief executive Steve Rosich said: "The club is aware of the matter and has informed the AFL.

"We are treating it very seriously. We are currently gathering all relevant information and will make further comment when we are in a position to do so.

"There will be no comment from the club until that time."

Geelong's Mathew Stokes was suspended until round eight earlier this year after being found with one gram of cocaine.

He pleaded guilty in court to possession and was placed on a 12-month good behaviour bond.

The investigation into Johnson has the potential to halt the Dockers' momentum after the club started the season in a blaze of glory with six wins from eight matches.

Johnson, who has played 92 games for the club since making his debut in 2005, has previously prided himself at being an indigenous leader at the club.

The 25-year-old has played a key role in Fremantle's strong start to the season, playing in the forward line and as a back-up ruckman to Aaron Sandilands.

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