Should Haller and Anderson both fail fitness tests then Pellegrini would be forced to drastically change his team, there is also a good chance that Aaron Cresswell could lose his place to Arthur Masuaku after a poor performance against Man City.
With all these factors in mind, this is my predicted line-up for Brighton.
Starting XI: Fabianski, Fredericks, Diop, Balbuena, Masuaku, Rice, Wilshere, Fornals, Lanzini, Yarmolenko, Antonio
Bench: Roberto, Ogbonna, Cresswell, Snodgrass, Hernandez, Ajeti, Zabaleta
The Hammers have not beaten Brighton since 2012 when they came away 6-0 winners in the Championship with a hat trick from Ricardo Vaz Te, one from Kevin Nolan, One from Carlton Cole and an own goal.
The last game ended a 2-2 draw at the London Stadium in January this year with Marko Arnautovic scoring both West Ham goals in a space of two minutes after Brighton were up two-nil in the space two minutes.