McDermott’s contract, which had 15 months to run, has been cancelled and not paid up, with the 24-year-old believed to have returned to his home in Ireland.
Signed by former boss Lee Bradbury in January 2012, McDermott’s career at Dean Court nosedived shortly after he had completed a £175,000 move from Huddersfield.
The Dubliner, who made 11 appearances for Cherries during a loan spell from Manchester City in 2011, was disciplined after missing the team coach to Bury in April 2012.
Just a month earlier, McDermott had also been fined £1,500 and banned from driving for 18 months after pleading guilty to being nearly twice the drink-drive limit.
Hauled off at half-time following a dismal showing during a 4-0 defeat at Swindon in Paul Groves’s penultimate game in charge, McDermott was given a clean slate following Howe’s arrival in October 2012.
But despite playing six times under Howe, he quickly fell out of favour and made his last league appearance as an 88th-minute substitute during a 3-0 win over Yeovil on Boxing Day 2012.
Although McDermott was handed another chance at the start of this season, featuring in League Cup ties against Portsmouth and Watford, he again failed to make an impression.
McDermott, who was believed to have rejected a number of offers to go on loan, had been training with the development squad until his stay at the club was brought to an end.
Boss Howe told the Daily Echo: “Donal wanted to go back to Ireland and we agreed to that. It did not work out for him here and the club has moved on. We wish him all the best in his future career and we now look to reshape our squad for next season.
“As a player, Donal has undoubted ability but we did not really see it on a consistent basis and it has been frustrating for him and us that it did not work out. Hopefully, he will get his career back on track.
“I firmly believe everyone deserves an opportunity. You can’t judge people on their past, you have to judge them on what they deliver for you and we did that with Donal. We gave him a clean slate but, unfortunately, it did not work out.”