Mike Tyson was scheduled to undergo surgery on Monday to repair a torn knee cartilage the former world heavyweight champion suffered during last week's stunning fourth round knockout loss to Danny Williams.

The 38-year-old Tyson is believed to have torn the complex lateral meniscus in his left knee during the first round of his fight against his unheralded British opponent.

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Richard Emerson was to perform the arthroscopic surgery in Phoenix, Arizona.

"Under normal circumstances the pain and locking that occurs with this injury would make it impossible for the athlete to continue and he would have to be taken out of the game or the boxing match on a stretcher or with assistance," Emerson said.

"I'm shocked that Mike was able to box for three more rounds after the injury occurred and that he was able to walk away from the ring."

A 9-1 underdog, the 31-year-old Williams improved his record to 32-3 with Friday's victory over Tyson in Louisville, Kentucky.

"It explains a lot," Tyson advisor Shelly Finkel said of the injury.

"Once he lost the ability to pivot, turn, or move laterally, much less put pressure on his left leg, he lost the ability to throw anymore meaningful right hands which had been so effective up to the point of the injury."

Tyson's record fell to 50-5-2 with the loss.