Irishman Quinn has not played since November because of injury
Oxford have released eight players, including former captain Barry Quinn.
Quinn joins defender Chris Willmott, pacy striker Yemi Odubade, midfielders Eddie Hutchinson and Craig Nelthorpe in not being offered a new deal.
Midfielder Phil Trainer, defender Matt Day and young striker Matt Taylor will also be leaving the club.
Chris Carruthers and Joe Burnell have been transfer-listed, and loanees Lewis Haldane and Craig Farrell return to Bristol Rovers and York respectively.
Defenders Kevin Sandwith and Shane Killock, signed on short-term deals from Weymouth and Huddersfield respectively, will be offered longer contracts.
United have also confirmed they are in talks with Sheffield United youngster Adam Chapman about a long-term deal after a productive loan spell at the Kassam Stadium since January.
I can't fault the attitude of those we have released, but we have to move forward, raise the bar a little, and we have some very exciting players in our sights for next season
Oxford boss Chris Wilder
Quinn, a former Republic of Ireland international, was United's longest serving player, having joined the U's in 2004 and had made 199 appearances for them.
The 29-year-old defender had been sidelined because of injury since November, before Chris Wilder's appointment as manager.
Willmott, Odubade and Quinn were three of only four players still at Oxford since their relegation from the Football League in 2006, leaving keeper Billy Turley as the only remaining representative from their league days.
Midfielder Hutchinson joined United the summer after their relegation and was the player not properly registered, which led to United's five-point deduction and their failure to reach the play-offs.
Winger Nelthorpe joined United on a short-term deal from Doncaster in January and impressed in stages, although his discipline was called into question following a red card in February's costly defeat by Torquay.
Trainer has been on loan with Telford this season, while Day and Taylor were not first-team regulars this season.
Wilder told the club's website: "I can't fault the attitude of those we have released, but we have to move forward, raise the bar a little, and we have some very exciting players in our sights for next season."
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