Ronnie O'Sullivan will not defend his world title next year after abandoning plans to return to the snooker tour because of "personal reasons," casting doubt on his future in the sport.

World Snooker chairman Barry Hearn says the 36-year-old Englishman "has decided to withdraw from any events he has entered, and he will not be playing for the rest of this season."

The mercurial O'Sullivan, who battles depression, won his fourth world title by beating Ali Carter in the final at the Crucible Theatre in Sheffield in May. A fluent break-builder, he is widely regarded as the most naturally talented player in the history of the sport, but his career has been dogged by controversy.

O'Sullivan took a sabbatical after the worlds and has only played in one low-profile tournament since.