"George, Mike Tyson hits so hard!!"
That was the WARNING Muhammad Ali gave to George Foreman around 1987 ... when a 40-year-old Foreman was considering a boxing comeback after a 10-year hiatus.
"George, that Mike Tyson can hit! That's punching power there!"
Foreman tells the whole story to TMZ Sports ... explaining how Muhammad was like his "big brother" and tried to advise him to stay away from Tyson, who was DESTROYING people at the time.
"It was like a warning, 'Don't do that George!