The news came today after Thommo went for a scan on a calf strain, which forced him to be substituted against Aberdeen at the weekend.
The Geordie has been immense for Celtic this season, and will be a big loss in the next few games.
Our biggest blow is that he will miss out against Anderlecht in the Champions League next Wednesday.
Martin O'Neill may choose to play Michael Gray in his place, but Liam Miller could also be looking for a starting slot against the Belgians and Kilmarnock this weekend.