West Ham right-back Carl Jenkinson suffered a 'significant' knee injury in the 2-2 draw with Manchester City last weekend.
Jenkinson, 23, who is on loan from Arsenal, had to be replaced when he injured his left knee conceding a first-half penalty at Upton Park for a foul on Sergio Aguero.
The Hammers say Jenkinson will see a specialist in London on Wednesday.
He was replaced against City by new signing from Leeds, Sam Byram.
No further details were given on the type of knee injury sustained, nor any timescale on Jenkinson's recovery.