Nicky Summerbee quit Sunderland yesterday then confessed he was baffled by Peter Reid's decision to freeze him out.
"I don't know why he treated me like he did," said Summerbee, who is ready to kick-start his flagging career at Bolton.
The former Manchester City winger has signed a six-month contract with Sam Allardyce's First Division high-flyers.
Summerbee was squeezed out by Sunderland boss Reid following a bust-up last season.
Reid has refused to select the 29-year-old forward this term and the situation spiralled into a pit of despair for the wide man. Summerbee was refused the opportunity of training with his teammates and he ended up packing his bags to return to his Manchester home midway through the season.
Sunderland have agreed to grant skipper Michael Gray a testimonial following his ten years' service.
Gray is Sunderland's longest-serving player and Reid said: "He has been a great servant and fully deserves a benefit game."
Gray, 26, signed for Sunderland as a 16-year-old. He was made captain last summer. The game is likely to form part of Sunderland's preparations for next season.
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