Cahill was replaced after just 13 minutes of the 2-0 defeat at Craven Cottage, a move that David Moyes believes was pivitol to the flow of the game.
"Tim's injury played a big part and we didn't look quite so good after that," Moyes said. "We didn't quite get to grips with it. He (Cahill) has got a back injury - he's walking but he's very sore so we'll have to see."
Since then Cahill has been very sore, and at this stage it is not clear if he will be fit for the crucial game on Saturday, which Everton simply muct win.
"It is a case of wait and see," said Everton physio Mick Rathbone.