AFL UMPIRES have been instructed to penalise players who slide into contests if there is contact below the knee and the risk of injury.

AFL football operations manager Adrian Anderson has written to all clubs to clarify the issue of sliding and rough conduct, warning of the potential for season-ending or even career-ending injuries.

Anderson said on Thursday players had a duty of care to opponents to not slide into a contest with their knees or feet first when there was potential to cause injury.

It was the AFL's view that some free kicks should already have been paid this season against players for sliding into contests, and Anderson said that given recent tribunal decisions the League would re-examine its guidelines around rough conduct in serious cases where injury may occur.

Both North Melbourne's Lindsay Thomas and Fremantle's Greg Broughton have successfully challenged match review panel penalties for sliding into contests that caused injury to Sydney Swan Gary Rohan and Gold Coast's David Swallow respectively.

Anderson said the AFL and the Laws Committee had last year identified sliding into contests as an emerging tactic and had notified all clubs in its pre-season DVD of its concern about the potential for serious injury to players.

He said the practice had become more prevalent in the early part of the season and medical advice to the AFL was that the potential for serious injury would continue to rise.

"The AFL's primary concern around the Laws of the Game continues to be the safety of our players," Anderson said.

"It is not illegal to slide to contest the ball, but players must be aware of the potential for injury if they slide into an opponent's knees or ankles.

"Our medical advice is that sliding into contests has the real potential to result in season-ending, or even career-ending, injuries, and that is something that no-one in the game wants to see."