The young keeper who was thrust into first-team action in City’s Emirates FA Cup Third Round tie against West Bromwich Albion in 2016.
O’Leary appeared for the second half at the Hawthorns following an injury to Frank Fielding and also featured in the replay at Ashton Gate.
The City academy graduate was sent on loan to National League North side Kidderminster Harriers in March 2016 to further his development and spent last season on loan at National League South outfit Bath City, excelling for the Romans.
O`Leary will be available to manager Mark Yates for Saturday’s home game with Gateshead.