Watford captain Troy Deeney has been ruled out for several weeks after undergoing minor knee surgery, the Premier League club said on Thursday.
Deeney, 31, started Watford`s opening two league defeats against Brighton and Hove Albion and Everton.
The club confirmed the surgery was successful but did not disclose how the injury was sustained.
"We will miss Troy because he is a very important player for us but I know he will be supporting us in the next games," Watford boss Javi Gracia said in a statement.
"I am looking forward to seeing him back as soon as possible."
Watford will look to record their first points of the league campaign on Saturday when they host West Ham United, who are also without a win after two games.
Following a 5-0 thrashing by defending champions Manchester City on the opening weekend, West Ham recovered well in a 1-1 draw at Brighton last weekend.
While supporters expect the club to compete for European qualification spots, manager Manuel Pellegrini has refused to set early-season targets.
"I`ve said from the beginning we don`t have a target for this season. We must try to improve," he said.
"We know what the Premier League is. We need to play every game as a final and, after that, we shall see where we finish."
Playmaker Manuel Lanzini has emerged as a bright spark in the West Ham midfield in the opening two games and Pellegrini confirmed the club are determined to extend his contract.
Lanzini, who has worked his way back from a knee ligament injury last year, has only 12 months left on his existing deal but West Ham have the option to extend it by two years.
"Manuel is a young player who has been committed to this club," Pellegrini said. "He is happy here and I hope he stays here for a long time."