Second-round opponent Ricky Walden was handed a bye to the quarter-finals as a result.
The pair were due to face on Friday night, with tournament organisers informed of O'Sullivan's withdrawal earlier in the day.
Snooker
Xiao stuns Trump in Galway
16/03/2012 AT 18:53
Walden faces Stephen Maguire in the last eight in Ireland.
Scottish Open
'He was struggling' - Robertson on his win over Jain
8 HOURS AGO
Scottish Open
'Can't believe what I've just seen' - Robertson's remarkable escape in win over Jain
8 HOURS AGO