"Leighton has got a fracture in one of the bones in his right foot," said Toffees boss Roberto Martinez.
"It could mean anything from missing six weeks to being back in 10 days. It depends how the fracture heals."
Martinez, speaking to the Everton website, added: "It's in such a specific spot and we're going to see how [the injury] reacts.
"We need to see how it develops."
Baines has played in every game for Everton this season and has started each of their 12 league games and scored twice.
He has also made five appearances for England as he challenges Ashley Cole for the first-team berth in the national side.
Leighton Baines: Pat Nevin on the 'underlapping' full-back
Baines's absence will be a blow for Martinez, whose side are seventh in the Premier League and one point off the top four ahead of testing trips to Manchester United and Arsenal in their next three games.
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