Ronnie O'Sullivan says he will not defend his Champion of Champions title after withdrawing to look after his "mental health".
O'Sullivan, who has won the competition a record four times, beat Judd Trump 10-6 in last year's final.
Ding Junhui will replace the seven-time world champion, who was due to face Zhang Anda, in Bolton on Wednesday.
"Mentally I feel a bit drained and stressed," wrote O'Sullivan in a post on social media.
"I want to look after my mental health and my body. I'm sorry to all the fans but I'll be back stronger."
China's Zhang recently defeated O'Sullivan at the English Open and again on his way to claiming the International Championship - his first ranking event win.
Current world number one O'Sullivan also pulled out of October's Northern Ireland Open in Belfast due to "medical reasons" and has previously spoken of well-documented issues with drink, drugs and depression.
Hawkins cruises into semi-finals
On the table, meanwhile, Barry Hawkins secured his spot in the semi-final with two commanding displays on Tuesday.
The 44-year-old made two century breaks on his way to a comfortable 4-0 opening win over world champion Luca Brecel, before later beating Robert Milkins 6-2.
Milkins had earlier overcome Mark Williams 4-2.
Victory for Hawkins means he joins Mark Allen in the last four.
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