The BBC pundit took to Twitter during the Europa League clash.
The Bhoys surrendered a 2-0 lead against the Turkish side and it is the second Europa League game out of two that has seen Ronny Deila's men draw after leading.
It depends on how you see it, though, either cup half empty or cup half full.
During the game, BBC pundit Sinclair, who has made it clear he has a soft spot for Celtic, praised Forrest for his role in the Bhoys' second goal.
He did, however, single out Celtic's weakness in defence.
Forrest got too much for the fullback 2-0 #celfcb hail hail— Trevor Sinclair (@trevor8sinclair) October 1, 2015
Disappointing to concede, pretty obvious defending a clean sheet has been a huge problem this season #celfcb— Trevor Sinclair (@trevor8sinclair) October 1, 2015
Sinclair also reserved praised for young Kieran Tierney, who performed well during his side's Europa League clash.
Celtic currently find themselves second in Group A on goals scored, which is a good position to be in after two draws.
The fact the Bhoys dropped points at home is evened out by the fact they earned one away from home.
Deila's men will know they need to do better at Parkhead, though, especially from a winning position. Molde top the group on four points after drawing with Ajax.