West Ham defensive pair Sam Byram and Winston Reid are out for the season.
The defensive duo suffered their injuries in the Hammers' painful 4-1 defeat away to relegation rivals Swansea at the weekend, says the Mirror.
New Zealand international centre-back Reid had to go off on a stretcher just 27 minutes into Saturday's game at the Liberty Stadium, after damaging ligaments in his right knee in an awkward penalty box fall.
And his emergency replacement, right-back Byram, then suffered an ankle injury that is also expected to keep him sidelined long term.
The two injuries are a major setback for boss David Moyes with West Ham still in relegation danger — just three points outside the bottom three after losing three out of their last four top flight games by a combined score of 11-3.