The attacking midfielder joined the Bluebirds in the summer.
The 29-year-old spent last season at Farnborough, helping them win promotion to the Evo-Stik League South Premier via the Evo-Stik South East play-offs.
Donnelly began his career at Queens Park Rangers, coming through the ranks at Loftus Road before making his debut in the Football League as a 16-year-old in 2004.
In total, he made fourteen first-team appearances for the R`s before leaving in 2007.
Donnelly has also had spells at Aldershot Town, Swansea City, Wycombe Wanders, Southend United, Havant & Waterlooville and Margate before joining his home-town club Farnborough last term.
After discussions over the past couple of weeks it’s been agreed mutually that Donnelly will leave the club with immediate effect.
Manager Mark Collier said: “Scott has found game time very limited. Personally, I don’t think we saw the best of Donners, who struggled a little with fitness. But he was a pleasure to work with and I certainly wish him very well at his new club”.
(Photo: Don Blandford)