O’Leary has been at the club on professional terms since 1995, spending just a few weeks away from the club on loan at Cheltenham in 2006.
But his contract has expired with the club, and no official news has been released regarding a new deal for the 31 year old.
The Welshman made just a single appearance – as a substitute – last season in the FA Cup at Histon, when we won 2-1.