Watford will be without Senegal international Ismaila Sarr for at least a month because of injury.
The injury puts his participation with Senegal at the Africa Cup of Nations, which begins on 9 January in Cameroon, in doubt.
The Senegalese winger has a knee ligament injury which the club say will be scanned again in about a month.
Sarr went off after 68 minutes of the 4-1 win over Manchester United on 20 November and missed the subsequent 4-2 defeat at Leicester City.
Sarr has made 34 appearances for Senegal since his debut in January 2017, scoring 6 goals. Senegal—2019 AFCON runners-up—are in the same group with Guinea, Malawi and Zimbabwe.