At first inspection, Geelong utility Paul Chapman's hamstring strain seemed so minor he was not expected to miss any AFL action.

But the injury has proved far more problematic than expected, with the three-time premiership star a real chance of being forced to sit out a fourth straight match on Saturday night against Collingwood.

It has prompted the Cats' medical staff to alter Chapman's rehabilitation program to ensure that when he does return, it will be at 100 per cent fitness.

"I'm not going to say that I'm very confident (he will play against the Magpies) because I've just been saying it every week and it's clearly a more-complicated issue than was first thought," Geelong coach Chris Scott said on Tuesday.

"I can categorically tell you it's not a severe hamstring strain.