Joe Rogan to Georges St-Pierre -- Stay Retired ... Don't Be the Next Chuck Liddell

Georges St-Pierre should hang up the gloves forever ... rather than risk a pathetic, washed-up comeback attempt like Muhammad Ali, Sugar Ray Leonard, and Chuck Liddell ... so says UFC commentator Joe Rogan.

Joe was in Calabasas when we asked if he thinks GSP will ever return to the octagon. Rogan told us "no one knows but him" ... but added that he should probably just call it quits.

According to Rogan, studies have shown that Georges was blasted with over 800 head shots during his long run as welterweight champ ... and suggested he could be struggling physically, as well as emotionally.