The left-back had to be substituted early in the second half of Saturday's Merseyside derby with a toe problem and requires further tests to identify the full extent of the injury
Baines was forced to withdraw after 50 minutes of the pulsating 3-3 draw against Liverpool at Goodison Park, with manager Roberto Martinez now anxiously awaiting the results of medical checks on the 28-year-old.
A breathless opening 20 minutes saw Liverpool move 2-1 ahead as Philippe Coutinho and Luis Suarez efforts sandwiched Kevin Mirallas's close-range finish.
Romelu Lukaku's double looked to have sealed Everton the points, but Daniel Sturridge scored a last-gasp equaliser, and Baines' injury left Martinez with a further headache.
Martinez told the club's official website: "We didn't want Leighton to leave the pitch but we had to adapt.
"We need to assess him because it will be a big miss for us if we lose Leighton.
"We are going to have an X-ray and see how it is, but I have never seen him come off a football pitch and it takes a lot for him to come off.
"We couldn't afford to risk leaving him on, but in the same manner we need to make sure it isn't a serious injury."