David Haye has suffered a torn bicep, forcing him to postpone his heavyweight rematch with Tony Bellew.
The British pair were slated to do battle for a second time on December 17 at London's O2 Arena.
Bellew beat Haye at the same venue in March, aided by the former heavyweight world champion suffering a serious ankle injury mid-bout.
Haye said in a statement: "Despite the recent injury rumours, I was in perfect condition with an incredibly strong training camp, currently weighing lighter than I have for more than five years, I couldn't wait to get back in the ring. I was ready to rewrite the ending of the Haye Bellew saga.
"Unfortunately, after a freak accident during a stair conditioning session, which I've done with no incident hundreds of times, I lost my footing, slipped, so instinctively grabbed the bannister to stop myself toppling down the stairwell, in doing so I somehow managed to damage my bicep in the process.
"This afternoon I underwent a procedure to repair it, this was pretty straightforward and my doctor and physiotherapist have no doubt that not only will I make a full recovery but will be able to be back in the gym to start my arm rehabilitation in two weeks."
Haye suggested that the pair will attempt to reschedule the fight for March 24 or May 5 in 2018.