The Belgium international appeared to be in considerable pain after he was caught by a strong challenge from Jordon Mutch late in the Merseyside club's 3-1 Premier League win at Goodison Park.
Mirallas had scored Everton's second goal with a deflected free-kick shortly before the break after Ross Barkley opened the scoring with a stunning individual strike.
Steven Naismith added a third goal before Bobby Zamora was on target for Harry Redknapp's side, who remain without a point away from home this season.
Victory for Everton moved them above neighbours Liverpool into 10th spot, but boss Roberto Martinez fears the three points may have come at a cost.
He told Sky Sports: "Kevin is the real negative, he has a really bad ankle. We will scan it in the morning and it was a real disappointment to see him carried off at the end."
Martinez was full of praise for Barkley's fine solo goal and was pleased with the manner in which the young midfielder took on the responsibility of playing in a deeper role in the absence of the suspended Gareth Barry.
The Spaniard added: "The difference today was how clinical we would be in front of goal and I'm pleased with that.
"The first goal [from Barkley] is as good as it's going to get in terms of individual quality and how to break lines of pressure.
"The big encouragement working with Ross is how quickly he takes new concepts on."
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