In the 71st minute of the Hammers' win over the Blues, Zouma was replaced by Fornals.
Kurt Zouma is set for a spell on the sidelines after he injured himself in the win over Chelsea.
The club have not set a timetable for his recovery, despite the fact that he had a Scan on Monday.
The knee injury that forced Angelo to miss the rest of the season was picked up in November.
The lack of defensive options may prompt David to move for reinforcements in January.
Since his summer move to West Ham, Zouma has started 11 of the Hammers' 15 league games, playing a key role in their surge to fourth place.
With the departure of veteran centre-backs such as Ogbonna and Reid, and the fact that only two fit specialist centre-backs are available, it's no wonder that David Moyes has only two fit specialist centre-backs.
Ben Johnson is set to return sooner than Zouma because he has a low-grade injury.
