Everton say defender Ramiro Funes Mori is likely to miss the rest of the season after suffering a torn meniscus playing for Argentina against Bolivia earlier this week.
The Toffees, who face Liverpool in the 228th Merseyside derby on Saturday, have already lost right-back Seamus Coleman for several months after an horrific double fracture of his leg playing for the Republic of Ireland against Wales.
Coleman's clubmate James McCarthy also aggravated a hamstring injury in the warm-up to that game.
"It has been confirmed that the defender suffered a torn meniscus in Argentina's 2-0 defeat to Bolivia on Tuesday evening," said a statement from Everton.