West Ham striker Marko Arnautovic has been ruled out for a month with the hamstring injury he suffered in Tuesday's 3-1 win over Cardiff.
The Austria international will miss the Christmas period, although he could be available for the FA Cup third round tie against Birmingham in January.
The 29-year-old has scored five goals in 13 league appearances this season.
"We know how important Marko is for our team," said West Ham boss Manuel Pellegrini.
"We have too many players injured in a month that we have to play seven games and then in January, six more games.