There was initially concern the 26 year old may have suffered a broken bone.
"We have mixed feelings because we feared the worst when that challenge happened," said boss Roberto Martinez.
"We thought it was a fracture and to have a fracture at this stage of the season would have been devastating for Tom because his form has been terrific.
"He has got ligament damage and the next step will be to see how long he is going to be out. But clearly it's good news from when we saw Tom falling to the ground."