O'Sullivan, who is suffering from glandular fever, was due to face Ricky Walden in the last 16 of the tournament, tonight at the Bailey Allen Hall in Galway. However World Snooker was advised of his withdrawal this morning.
Walden receives a bye to the quarter-finals.
The tournament, which is the culmination of the Players Tour Championship series, runs until Sunday.
Ball by ball scoring and results from tournaments