Barry Nicholson has rejected the offer of a new contract from Aberdeen as manager Jimmy Calderwood also announced a clearout of six other players.
Keepers Derek Soutar and Greg Kelly, defenders Richie Byrne and Dave Bus and strikers Jonathan Smith and Steve Lovell are not being offered new deals.
Striker Lee Miller has yet to decide whether to accept a contract offer.
"It's obviously disappointing that Barry has decided to move on," Calderwood told his club website.
"But, to be honest, it did not come as a huge surprise."
It had long been hinted that the 29-year-old midfielder would follow Chris Clark and Michael Hart by accepting higher cash offers from English clubs.
"As far as Lee Miller is concerned, he is leaving his options open"
Clark left for Plymouth Argyle while Hart headed for Preston North End during the January transfer window.
And Calderwood had warned that his budget for next season would be further curtailed by Saturday's surprise defeat to Queen of the South in the Scottish Cup semi-final.
"As far as Lee is concerned, he is leaving his options open and, while I'm hopeful that he will decide to stay, we have to obviously prepare a squad for next season in mind," said the manager.
Forward Sone Aluko will return to Birmingham City at the end of his loan, while the future of midfielder Josh Walker has yet to be decided by Middlesbrough.
Calderwood is hopeful that both will be back at Pittodrie next season.
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Midfielder Stuart Duff and defender Alan Maybury, who both signed short-term deals in January, have been given until the end of the season to prove they are worth new contracts.
Calderwood denied that the announcement was a knee-jerk reaction to being knocked out of the cup by First Division Queens.
"It's just time to freshen up the side," he said.
"Some of the boys are out of contract anyway.
"I have been looking at bringing in new new players for months.
"You always need to be freshening things up."
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