With Stevie Crawford moving to Plymouth and Craig Brewster out injured, Hay's options up-front were very limited with only Noel Hunt and Billy Mehmet being potential candidates for the job.
Shortly before Donnelly appeared as a second-half substitute in the friendly against Clyde, the striker - capped 10 times for Scotland - put pen-to-paper on a one-year deal.
After an injury ravaged career at Celtic and Sheffield Wednesday, Donnelly performed consistently well for St. Johnstone in season 2003/04 playing over 40 times and scoring 9 goals mainly from a midfield position.
Speaking of his new signing, manager Davie Hay said "I am sure he will be a welcome addition to the squad."