Danny Ings will be out for several weeks after picking up a knee injury on his West Ham debut, according to reports.
The English striker joined the Hammers from Aston Villa for £12million on Friday and made his debut in a 2-0 win against Everton on Saturday, replacing Michail Antonio for the final 20 minutes.
And as reported by the Guardian, Ings' minor knock after a late tackle in the Toffees clash will keep him on the sidelines, alongside fellow injured forward Gianluca Scamacca.
Only three Premier League teams have currently scored fewer goals than West Ham's 17 so far this season, with Ings' arrival hoped to solve their goalscoring problem.
In that context and with Scamacca out too, his latest setback will be a blow to struggling manager David Moyes.
Former Southampton and Liverpool striker Ings is ineligible for their FA Cup tie at League One Derby County on Monday 30 January, but is expected to miss their next two league games against Newcastle and Chelsea too.
He may return against Tottenham on February 19, but it is believed their home game against Nottingham Forest the following week is a more likely match for his return.
Ings' current issue is not thought to be related to two long-term knee ligament injuries suffered earlier in his career.
West Ham's win against Everton saw them rise to 16th in the table - one clear of the relegation zone.