Nathan Cleverly has had to delay his cruiserweight debut for the second time because of injury.
The 26-year-old's planned debut at the new weight against Daniel Ammann in November was put off as
Cleverly had a back injury.
Another back problem has now ended Cleverly's fight with Illunga Makubu, scheduled for 1 February in Monaco.
Cleverly moved up in weight after
losing his WBO light-heavyweight title
to Sergey Kovalev in August.
Welshman Cleverly, who has won 26 of his 27 fights as a professional, had hinted at retirement after the defeat to the Russian before announcing he was going to step up in weight.
"He has sustained a minor injury and will not be fighting in Monte Carlo on February 1st, and we are about to reschedule a fight for him," said Cleverly's promoter Frank Warren.