Watford's Nigeria midfielder Peter Etebo has been ruled out for four to five months due a torn thigh muscle, the Premier League club said on Thursday.
The 25-year-old Etebo, on loan from Championship side Stoke City, suffered the injury as a substitute in Watford's 1-1 draw at home to Newcastle United at the weekend, leaving his participation in January's Africa Cup of Nations in doubt.
"I am very sad about this - when one of our players has a big injury. It is a problem for us and that is all you can say," said Watford manager Xisco Munoz.
"It is a moment to try and give the best recovery for him ... he had a very good attitude for our team."
Watford, who are 12th in the league with seven points, travel to 18th-placed Leeds United on Saturday.