Everton expect to be without Jarrad Branthwaite for around a month.
The teenage defender hurt his ankle in Wednesday night's Carabao Cup tie with Salford City and was forced off after 25 minutes.
Branthwaite underwent scans yesterday which are understood to have revealed torn ligaments in his left ankle.
The Blues believe Branthwaite will be sidelined for around four weeks.
Carlo Ancelotti heads into tomorrow's game with West Bromwich Albion with only Michael Keane and Yerry Mina as his only fit senior centre-halves.
Mason Holgate (toe) has missed the opening two games of the season and faces an extended spell on the sidelines.
Ancelotti confirmed, on Wednesday night, that Holgate has avoided the need for surgery but was unable to put a timescale on his return.
The Everton boss said that the club will look to add defensive reinforcements with Fikayo Tomori under consideration for a loan from Chelsea.
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