Pound-for-pound king Vasiliy Lomachenko suffered a torn labrum in his right shoulder during his knockout of Jorge Linares to win the lightweight world championship on May 12 and will undergo arthroscopic surgery on Wednesday in Los Angeles, Top Rank promoter Bob Arum told ESPN.

Lomachenko told ESPN on Tuesday that he suffered the injury during the second round of the fight. He said his right shoulder popped out of place and then back in and gave him trouble for the remainder of the bout.

"I couldn't use my right arm to throw my right hook, and it was very uncomfortable to continue my fight," said Lomachenko, speaking to ESPN immediately following his examination by orthopedic surgeon Dr. Neal ElAttrache at the Kerlan Jobe Orthopedic Clinic in Los Angeles.

ElAttrache will perform the 60- to 90-minute arthroscopic procedure on Lomachenko. After examining the fighter, including giving him an MRI, ElAttrache told ESPN: "There is clear evidence that he had a recent dislocation of the shoulder, and the most common injury that happens when there is a dislocation is a tear in the labrum. His is pretty extensive. A typical tear usually goes from about 2 o'clock if you're looking at the face of a clock down to about 6 o'clock. His goes almost all the way around. I would say he has significant instability of his right shoulder."

ElAttrache estimated that if all goes well with the surgery and Lomachenko's rehabilitation that he could return to training in early October and be ready to fight in early December.

"None of these things are carved in stone," ElAttrache said. "The most important thing is to protect him and allow this to heal properly. With what I'm seeing now that's the timetable if things go perfectly."

Arum, who was with Lomachenko and manager Egis Klimas at the exam, said that if there are no complications, Lomachenko will return to the ring in the main event of a Top Rank Boxing on ESPN card on Dec. 8.

In a highly competitive and exciting fight, Lomachenko (11-1, 9 KOs) knocked out Linares to win the lightweight world title at Madison Square Garden in New York, but he had some struggles, in part due to the shoulder injury, including getting knocked down for the first time in his career in the sixth round.

At ringside after the fight, Arum said Lomachenko would make his first defense on Aug. 25 at The Forum in Inglewood, California, but last week he told ESPN that there had been a change of plans and that Lomachenko, who vacated his junior lightweight world title in order to defend his belt at lightweight, would not fight this summer.

Arum knew then that Lomachenko was having shoulder pain but declined to give a reason he wouldn't fight on Aug. 25 until Lomachenko had been examined by ElAttrache. Lomachenko had returned home to Ukraine after the bout but experienced continued pain in his shoulder.

"The shoulder popped out and then popped back in so he was able to finish the fight, but when he went back home it was hurting him and so he got an MRI in the Ukraine, and it showed the tear," Arum said. "He was making arrangements to take care of it over there and that's when Egis and myself said you have to come here [to Los Angeles] and have Dr. ElAttrache look at you and do the operation."

Lomachenko returned to the United States on Monday and then went to see ElAttrache, who is the team doctor for the Los Angeles Dodgers and Rams. He has treated boxers before, performing rotator cuff surgery on Manny Pacquiao following his loss to Floyd Mayweather in 2015 and also operating on former heavyweight world champion Vitali Klitschko and former welterweight titlist Andre Berto. Besides boxing, he has operated on NBA legend Kobe Bryant and New England Patriots quarterback Tom Brady, among many others.

According to Arum and Klimas, Lomachenko has had occasional pain in his right shoulder in the past but nothing severe.

"Every once in a while when he would spar, he'd have pain in the shoulder but then he'd ice it and then there'd be no problem," Arum said. "But this time it was different with the pain he was having in the fight and after the fight. So, obviously, Aug. 25 is out for his next fight and we're looking at Dec. 8. If the shoulder doesn't come around in time we'll have to postpone it, but we're looking at him being ready to go Dec. 8. But we know there are no guarantees."

Arum had hoped to match Lomachenko on Aug. 25 with fellow lightweight world titleholder Raymundo Beltran (35-7-1, 21 KOs), who won a vacant belt in February. Now, Beltran may defend his title against somebody else on that date and then, if he wins, meet Lomachenko in the unification bout on Dec. 8, Arum said.

The win over Linares gave Lomachenko, 30, a two-time Olympic gold medalist from Ukraine, a world title in his third weight division and the boxing record for winning world titles in three divisions in the fewest number of fights (12). He shattered the record of 20 set by Australian great and International Boxing Hall of Famer Jeff Fenech in 1988.

Lomachenko also is tied for the record for fewest fights needed to win a world title (three) and to win world titles in two weight classes (seven).