The AFL has become embroiled in another betting scandal, launching an investigation into Essendon assistant coach Dean Wallis.

The Bombers have confirmed Wallis - a dual Essendon premiership player - is at the centre of a probe into betting on a recent match involving his club.

He met the league on Friday morning, and the Bombers said he was "assisting the AFL's investigation into allegations relating to betting on AFL football".

"The club will continue to support Dean throughout the period of the investigation," Essendon said in a statement.

"The club will make no further comment at this time."

The investigation, which the AFL expects will take several days, promises an unwanted distraction for the Bombers leading into their finals campaign starting next week.

And if the allegations that an assistant coach has bet on an AFL match are true, chief executive Andrew Demetriou says it "defies belief".

The investigation comes at the end of a season in which Collingwood defender Heath Shaw was suspended for eight weeks for betting, and Magpies skipper Nick Maxwell was fined for breaking the league's strict anti-gambling rules.

"After what's transpired in the past few weeks, the actual notion that someone has had a bet on their own team seems incredible ... it defies belief," Demetriou told Melbourne radio station 3AW.

"Not wishing to pre-judge what may or may not occur, but if in fact someone has bet on their team again, after what has happened in the past few weeks, then you can only assume that this is a very serious issue."

Wallis, 42, is a development coach at Essendon and a former premiership teammate of Bombers head coach James Hird.

It is understood the bet under investigation involves a three-figure sum on a quarter quad bet - where a punter nominates the team leading at the end of each quarter, and the margin.

The AFL can suspend or fine those involved in the sport who are found guilty of betting on matches.

"Our integrity officer Brett Clothier is continuing that investigation today and, once he gets more facts and completes that investigation, we'll do what we always do and make that known publicly, if in fact that is true," Demetriou said.

"If there is something to answer for, we will make it public."

The reaction to the Collingwood betting scandal in July signalled loud and clear the AFL's stance on those involved in the game punting on the sport.

After four players including Adelaide's Simon Goodwin were fined or reprimanded in 2007 for betting on matches, tougher penalties were promised when the issue took centre stage again in mid-2010, this time involving club and match officials.

Port Adelaide coach Matthew Primus, then an assistant at the club, was suspended for two weeks after being found to have placed a $20 multi-bet on a match not involving his team.

Two interchange stewards, a goal umpire, a timekeeper and Western Bulldogs board member Geoff Walsh were also sanctioned after being caught up in that 2010 betting blitz.

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