Everton manager Carlo Ancelotti has confirmed midfielder Allan has sustained a hamstring injury.
The Toffees have enjoyed a good week, defeating Chelsea and Leicester City.
But losing the Brazilian is a blow to Ancelotti and his team, with Allan being stretchered off late against Leicester.
Ancelotti told reporters: "Yes, he had the problem and we have to check in the next few days how long he has to be out. I hope he can recover soon.
"We have back Seamus Coleman. Andre Gomes replaced Allan really well today.
"Unfortunately in this period injuries will happen.
"We have a busy time with a lot of games and sometimes this can happen."