O'Donnell, who was on trial at City for the 2003 pre-season games in Germany v Suhl and Fruth, collapsed just as he was about to be replaced near to the end of the game which Motherwell won 5-3.
The 35 year old, former Celtic and Sheffield Wednesday player, was treated on the pitch before being taken to an ambulance.
Motherwell later confirmed his death
Phil O'Donnell RIP