Everton manager Roberto Martinez is sending defender Leighton Baines is to see a specialist to determine the extent of his ankle injury.
The left-back was forced off in the second half of the 2-0 weekend defeat by Sunderland.
Martinez told the club website: "We're going to find out a bit more in the next two days. It was really, really painful in an area that has been a bit of a problem for Leighton.
"We'll get more clarity over the next 48 hours and clearly we'll address it once we get that information from the specialist."
The 30-year-old missed two matches in November with a hamstring problem and thigh and knee injuries kept him out for seven games in February and March. Baines was replaced by Luke Garbutt on Saturday.