Andy Ruiz Jr has undergone 'successful' surgery to repair his damaged knee ligaments he aggravated against Chris Arreola.
Ruiz Jr, 31, faces at least a further three-to-four months on the sidelines after being planted firmly on his backside by the former WBC title challenger during his comeback fight earlier this year.
The Mexican-American shocked the boxing world in June 2019 at Madison Square Garden in New York City when he knocked out Anthony Joshua in the seventh round, picking up the Englishman's WBA, IBF, WBO and IBO heavyweight world titles in the process, before waving the white flag six months later.
His team have confirmed Ruiz Jr's surgery to repair his damaged ligaments was a success in a huge boost to his chances of regaining the belts.
But his father refused to put a timeframe on his return after initial reports suggested he had been hoping to face Charles Martin in October.
"He underwent surgery on his right knee, he had been struggling with that knee for about three years," Andy Ruiz Sr told ESPN.
"He could not run very much, he could not do certain movements, he used gel to mitigate the pain, but it was not enough and he made the decision to get the procedure done, which was an arthroscopy.
"It was done by the same doctor who operated on Canelo [Alvarez], Pedro Lomeli Jaime."
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However, Ruiz Sr is increasingly optimistic about his chances of returning to the ring before the end of the year.
"They gave us hope that he would come back in December," he added.
"The physical trainer and the doctor told us that if everything goes well as it is now, then there is that possibility, but we will see when the time comes.
"For now we are happy that the surgery went well."