Everton manager David Moyes has been rocked by the news that star midfield man Tim Cahill will be out of action for three weeks.
The Australia international picked up the injury during his team's 2-1 Europa League win at home to Sporting Lisbon on Tuesday.
It was initially thought he would only miss the Premier League clash with Manchester United but, after further tests, it has emerged he has a grade one calf strain.
He will now miss the return leg in Lisbon next week to add to Moyes' woes.
The Toffees boss said: "Tim will be out for two to three weeks because he has got a calf strain.
"It is a grade one, it is not serious but I would be very surprised if he could make any of the games in this coming week."
He joins fellow midfield general Marouane Fellaini on the sidelines with the Belgian out for the rest of the season after injuring an ankle in the heated Merseyside defeat to Liverpool on February 6.
Meanwhile, defender Philippe Senderos will miss the contest despite making progress from his injury.
"Philippe is getting better but I am not sure yet if he will make the United game," Moyes added. "This game may have come too soon for him."