Carl Jenkinson could miss the rest of the season after the on-loan West Ham defender suffered a significant knee injury in Saturday's draw with Manchester City.
The 23-year-old, on loan at Upton Park for the second season in succession, will see a specialist later in the week and could face a lengthy spell on the sidelines.
It is likely the defender will return to parent club Arsenal for his rehabilitation, with West Ham offering an update on his injury through their website.
"West Ham United can confirm that Carl Jenkinson injured his left knee during the early stages of Saturday's Barclays Premier League fixture with Manchester City," a statement read.
"Unfortunately, it appears that Carl has suffered a significant injury and he will be assessed by a specialist in central London on Wednesday.
"A further update will be provided when the full extent of the injury has been confirmed."
Jenkinson has one England cap and enjoyed a successful year with the Hammers last season before rejoining for the current campaign.
It has proved less fruitful for both player and club, although he did score back-to-back Barclays Premier League goals in October, and manager Slaven Bilic has a ready-made replacement having signed Sam Byram from Leeds earlier in January.
Jenkinson, who joined Arsenal from Charlton in 2011, was forced off early on in the 2-2 draw at the weekend - a result which left the Hammers sixth in the table.
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