Everton left-back Leighton Baines will see a specialist to determine the extent of his ankle injury, manager Roberto Martinez says.
The England international is a doubt for Saturday's trip to West Ham after suffering the problem last weekend.
Baines, 30, was forced off during the second half of Everton's 2-0 defeat at home to Sunderland.
Martinez expects to discover the seriousness of the injury by Thursday.
"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," the manager told Everton's website.
"We'll get more clarity over the next 48 hours and clearly we'll address it once we get that information from the specialist.
"It's a situation where we need to find out exactly what's causing the pain.
"We want to find the solution so that Leighton can be pain free because it seems like it's a problem that's been developing over a couple of weeks now and we need to put it right.
"He'll see the specialist this week and we'll make sure that before Friday we know if he's going to be available for the squad against West Ham or not."