The Barcelona loanee was taken off on a stretcher after pulling up in the second half of Everton's 4-1 win over Fulham.
A statement on Everton's official website confirmed Deulofeu faces "a few weeks" on the sidelines, meaning he will miss a busy run of fixtures.
"Scans have now shown the extent of the soft tissue injury in his right hamstring, which is likely to keep him out for a few weeks," read the statement.
Deulofeu has made a big impression since arriving at Goodison Park on a temporary basis, having initially been eased into first-team action by manager Roberto Martinez.
Everton’s next match is against Swansea City on Sunday, the first of four games in 11 days.
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