Conor McGregor said his July 11 comeback against Max Holloway ended with ACL and meniscus damage after he landed awkwardly on a jump kick and could not continue.
The 38-year-old said the injury mirrors the one from his first fight with Holloway 13 years ago, but this time in the opposite leg.
McGregor had said last week he would undergo surgery and still hopes to return for the final bout on his UFC contract by summer 2027.
He also pointed to early recovery progress, saying he is walking without a crutch and has resumed light quad work under resistance.