Anthony Joshua has already been given a mandatory defence of one of his world title belts - just minutes after winning them back.
Joshua outpointed Andy Ruiz Jr to reclaim the WBO, WBA, IBF and IBO heavyweight straps with a classy display in Saudi Arabia.
But the WBO president has now ordered Joshua to defend against mandatory challenger Oleksandr Usyk within the next 180 days.
If he does not agree to meet the Ukrainian former cruiserweight king before June 4, he will be forced to vacate his belt, dealing a setback in the hopes of unifying the division by adding the WBC crown.
In the build-up to Joshua's clash with Ruiz, much was made of the prospect of the winner having to vacate at least one of their belts with mandatory challengers circling.
Kubrat Pulev is also the IBF mandatory which could be ordered, leaving Joshua looking likely to vacate the WBO strap if forced to give one up.
Usyk, who conquered the cruiserweight division, made his long-awaited step up in weight in October when he stopped Chazz Witherspoon in the seventh round.
If Joshua vacates the belt, he could face either Dereck Chisora or Joseph Parker for the strap, which would divide the belts further across the division.
After beating Ruiz Jr, promoter Eddie Hearn proclaimed Joshua is the "governor of the division", with the only belt he is yet to win being the WBC strap held by Deontay Wilder .
Hearn said: “This man has been responsible for the growth of British boxing. He has given everything to this sport.
“Tonight, in Saudi Arabia, he becomes a two-time champion of the world.
“They said he was all hype. He had to come back from humiliation at Madison Square Garden.
“Tonight, he’s the governor of the division.”
