Everton could be without on-loan Manchester City defender Eliaquim Mangala for the rest of the season.
Mangala had to come off before half-time in the 3-1 home win over Crystal Palace, and manager Sam Allardyce said he would be a "long-term" absentee amid fears he has damaged knee ligaments.
Allardyce, who has taken his side to Dubai for a warm-weather training camp, told Everton's official website: "Mangala, particularly, looks like its long-term, which is a great shame for him and for us as I think he was a very good addition to us."
Everton are expected to find out more about the extent of the injury in the next few days.
But Allardyce, whose side went on to beat Palace after Mangala's injury, remained upbeat about the remainder of his team's season.
Speaking about the benefits of the Dubai trip, he said: "We've been able to relax together and work hard together and I think it has helped bring relationships closer.
"Some are already friends and some will have made bigger friends with others and, of course, the big thing about it for us all is to get to know each other better - not just the players but the players and the staff as well."