Ronnie O'Sullivan has revealed his recent busy schedule has 'taken it out of him'.
The Rocket has made it through to the semi-final of the Masters for a 15th time but has admitted he has been suffering with a cold and loss of hearing in recent weeks.
O'Sullivan came from behind to beat Barry Hawkins 6-3 in Thursday's quarter-final at Alexandra Palace.
Hawkins led 3-2 but O'Sullivan won four frames in a row to win the best-of-11 clash.
Ronnie O'Sullivan has revealed he has been struggling in recent weeks
BBC
Neither player were at their best and O'Sullivan apologised to the crowd and Hawkins for his performance.
The 48-year-old is currently playing his seventh tournament since September last year, four of which have been in China.
And he admits the travelling has taken its toll on him.
Asked about his level of performance, O'Sullivan told the BBC: "Maybe I've played a lot since September.
"For me I've played a lot, travelled a lot. I've played a lot.
"Backwards and forwards from China, which takes it out of you.
"Trying to do everything can be hard and I think you can, especially at my age, it can take a little bit out of you.
"I don't know, I'm just trying to give you answers here, I still don't know the answer."
O'Sullivan then revealed he has been battling a cold in recent weeks and also lost his hearing during a tournament in China.
He added: "I feel alright. I think like everybody else in this country I've had a cold for about four weeks, lost my hearing as well in China.
"So not been too well but I think everybody's been like that."
O'Sullivan will play either Shaun Murphy or Jack Lisowski in Saturday's semi-final at Ally Pally.
Murphy and Lisowski will battle it out on Thursday evening for a place in the last four.
O'Sullivan pulled off a superb shot on the red to finish off the win over Hawkins.
But he admitted it was an otherwise poor performance.
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Ronnie O'Sullivan has been struggling with a cold in recent weeks
PA
He said: "I must have gone through another 25 cue actions.
"I managed to find one that seemed to be okay and I started to feel like I maybe could pot a few balls and that settled me down a little bit. Funny old game.
"I wasn't going to turn anything down. If it was on, I was going to go for it."
O'Sullivan claimed he brought Hawkins down to an even lower level than he was playing.
He conceded: "I just feel sorry for Barry.
Barry Hawkins was beaten 6-3 by Ronnie O'Sullivan at Ally Pally
PA
"He was playing good until he started playing me and I just dragged him down to probably the most awful standard of snooker.
"So I'm really sorry about that today but I'm just lucky to get through really, that's all I can say."