Everton goalkeeper Tim Howard will be out of action for up to six weeks because of a calf injury.
American Howard, 35, was replaced at half-time during the Toffees' 1-0 home defeat against Stoke on 26 December.
Spanish goalkeeper Joel Robles, 24, came on in that game and played in the 3-2 loss to Newcastle on 28 December.
Everton are currently 12th in the Premier League, five points above the relegation places with only one victory from their last seven league matches.
"Tim will be out for between five and six weeks," said boss Roberto Martinez. "It is an injury to his left calf. As a goalkeeper it's really unusual to get an injury by kicking a ball."
Robles signed for Everton from Wigan for £2m in July 2013, but has only played in the Premier League four times since that transfer.
Everton's only other goalkeeping options are 18-year-olds Russell Griffiths and Jindrich Stanek, who have both never played a senior game for the club.
"I thought Joel was very calm against Stoke and did well against Newcastle, but we will assess whether we need cover," added Martinez.
Midfielder James McCarthy will be assessed before Everton's trip to Hull on 1 January.
Howard, who has played 315 times in the Premier League for the Toffees, made 15 saves during USA's 2-1 defeat against Belgium in the last-16 of the 2014 World Cup, the highest-recorded total in one match in the tournament's history.
|Everton games Tim Howard may miss|
|1 Jan v Hull (A)||6 Jan v West Ham (H)||10 Jan v Man City (H)|
|19 Jan v W Brom (H)||31 Jan v C Palace (A)||7 Feb v Liverpool (H)|
|All games are in the Premier League, apart from 6 January in the FA Cup|