West Ham will not be able to recall Reece Oxford from his loan at Reading.
There is no clause in the contract to say that the 18-year-old defender can be brought back from the Championship club following injury to Winston Reid.
Reid is set to be sidelined for at least four weeks, meaning West Ham will have to make do with James Collins and Jose Fonte as a centre-back pairing.
It is understood the same situation applies to Reece Burke, who is on loan at Wigan.