Andre Ward has been forced to pull out of his light-heavyweight debut fight in Las Vegas on November 21 because of injury.
The WBA (Super) super-middleweight champion was set to make his debut at 175lbs in the co-feature at the Mandalay Bay alongside Miguel Cotto's WBC middleweight title bout with Saul Alvarez, but has been ruled out because of inflammation and pain in his right knee.
Ward's opponent had not been confirmed, although Colombian Alexander Brand was the most likely candidate.
"I'm extremely disappointed that I'm missing this opportunity on November 21, but at the same time, I'm encouraged," Ward (28-0-KO15) said in a statement released by Roc Nation Sports.
"Anytime I have had a minor or major setback in my career, by the grace of God, I've come back stronger and this will be no different. I'm looking forward to a big 2016. Thank you to all my fans for your support and patience."
Ward, 31, has fought just three times since beating Carl Froch in December 2011 to become one of the sport's top pound-for-pound boxers.
The Olympic gold medallist had a 14-month layoff after stopping Chad Dawson in August 2012, which was followed by a further 19 months out of the ring before returning in June to beat Britain's Paul Smith in California.
Roc Nation, which also promotes Cotto, is working to add a replacement fight to the event.
"We have no doubt that Andre will come back stronger than ever once his knee heals and that he will be a force in the light-heavyweight division," Roc Nation executive David Itskowitch said.
"We are working diligently to make an intriguing fight that will deliver a level of excitement commensurate with this great event."
Ward is expected to take on WBA (Super), WBO and IBF light-heavyweight champion Sergey Kovalev next year.