Phil Jagielka could miss Everton's FA Cup semi-final after hobbling out of Saturday's 1-1 draw at Watford, according to manager Roberto Martinez.
The centre-back picked up a hamstring injury in the stalemate at Vicarage Road, and was replaced by Ramiro Funes Mori in the 90th minute.
Everton have a busy schedule in the coming weeks with Premier League matches against Crystal Palace, Southampton and Liverpool before their cup semi-final on April 23.
Martinez remains unclear how many of those games Jagielka will miss, but hopes tests in the coming days will provide a clearer picture.
"It was a real negative when Phil felt his hamstring towards the end," the Spaniard told the club's official website.
"He will be assessed over the next 24 hours but it doesn't look good.
"Phil doesn't get injured that often, so when he asks to come off then that is a worry. He was holding his left hamstring and we will assess it overnight.
"It is too early to tell [whether he will miss the semi-final]. We have a period of five games in two weeks, but he is a serious doubt for Wednesday and Crystal Palace."
Everton will learn the identity of their semi-final opponents on Wednesday night, when West Ham play Manchester United.