Middlesbrough midfielder Julio Arca is facing at least two months on the sidelines after tests confirmed he damaged medial ligaments against Sunderland at the weekend.
The 26-year-old Argentinian was carried off during the first half of the 2-2 Premier League draw with his former club.
However, there was better news on strikers Tuncay Sanli and Mido, who limped off with shin and hamstring problems respectively, with both being given a chance of making Sunday's trip to Everton.
Manager Gareth Southgate told the club's website: 'We have ad some more positive news this afternoon.
'Both Mido and Tuncay have gone for scans and there's no significant damage, and both have a chance of playing on Sunday.
'However, the injury to Julio looks more serious. It's the medial ligaments in his knee and it looks like it will be at least two months.'