[Sporx]

I didn't know that about BW and Kraven.

I am thinking the comic book Ali, not the real world... where he fights a depowered Superman and an alien champion. Not sure that it matters, but the design could be a little "looser" on reality. I am open to whatever.

From Wikipedia:

The Superman vs. Muhammad Ali match is broadcast on intergalactic television to thousands of other worlds (with Jimmy Olsen acting as broadcaster). With the match underway, it soon becomes apparent that in battling with more or less equal strength, Ali is the superior fighter since Superman generally relied on his incredible strength brought on by Earth's yellow sun to deal with threats quickly. Superman takes a serious pummeling, but somehow refuses to fall down; he stays on his feet all through the beating. Finally, Ali stops the fight, intending to call for a technical knockout, but Superman then falls face-first on the canvas (making the knockout more than technical). Ali personally takes care of Superman and orders him brought back to Earth to recuperate; a move which leaves Hun'Ya pondering.

Now crowned Earth's champion, Ali is set to face Hun'Ya, and to everyone's surprise, the goddess Pallas Athena makes an appearance to relay "the rules of fair play" for this contest into the champions' minds. Rat'Lar then asks Ali to predict at what round the fight will end (Ali was known for predicting the round in which he would knock out his opponent). After some chiding, Ali predicts that he will knock the alien out in the fourth round ("He'll hit the floor in four!"). Once the match begins, however, Ali quickly starts to suffer from fighting the super-powered Hun'Ya.

Meanwhile, Superman's great recuperative powers have enabled him to make a speedy recovery. Disguising himself as Ali cornerman Bundini Brown, he steals into the Scrubb command ship and sabotages their space armada. In his showdown with the armada, Superman is again badly hurt, and is left drifting in space.

Miraculously, Ali gets a second wind. In the predicted fourth round, he not only knocks the alien champion out, but out of the ring as well. Yet after witnessing Superman's decimation of his forces, the Scrubb leader cries foul and decides to destroy the now helpless Earth anyway. Just as Rat'Lar is about to give the go-ahead to his backup forces, his own champion Hun'Ya becomes enraged at Rat'Lar's treachery and deposes him, stopping the annihilation attack.

Superman is rescued and once again revived. Hun-ya, the new Scrubb leader, makes peace with Ali, Superman, and all of Earth. The very end of the book shows Ali and Superman in a private moment. Ali reveals that he figured out Superman's secret identity as Clark Kent, but implicitly vows to keep it secret. The book ends with the two champions embracing and Ali proclaiming, "Superman, WE are the greatest!"