The former England manager was linked with a move to Cardiff in the summer but he went to Forest and it's all ended in tears.
Forest lost again yesterday, their 6th defeat from the 10 games played and McClaren walked out.
"I resigned - they don't share the ambition that I came for," he claimed.
Dave Jones is one of the names linked with the now vacant post but he's competing with former Forest heavyweights NIgel Clough, Stuart Pearce, Roy Keane and Martin O'Neill as possible successors to McClaren.
Yesterday Forest were beaten 3 - 1 at home by Birmingham and that followed a 5 - 1 defeat by Burnley.