Watford full-back Jeremy Ngakia will be out of action for at least four weeks because of a knee problem.
The 23-year-old suffered a "contact injury" during Saturday's 1-0 Championship defeat at Millwall.
He was taken off in the 66th minute of his comeback game, having been out of action since November because of an ankle injury.
"Now we need to make sure he recovers properly," head coach Valerien Ismael told the club website.
Watford are 12th in the table, 12 points outside the play-off places and six points above the relegation zone.