"He is going to have an operation on his hamstring and the biggest thing now is to get him ready for next season," Moyes told a news conference ahead of Sunday's league trip to Chelsea.
The 28-year-old has been blighted by rib and calf injuries during the campaign and Moyes said that the latest setback could be a recurrence of a previous knock.
"He picked up a hamstring injury at the end of last season and has never really recovered from that. In the short time that I've been here he's had a few pretty bad injuries. I hope we can get him back quickly for next season," the Scot said.
Midfielder Manuel Lanzini is a doubt for the clash at Stamford Bridge with a knee ligament injury.
West Ham are 14th in the league with 33 points from 31 games, five points above the relegation zone. Defending champions Chelsea are fifth with 56 points.
(Reporting by Shrivathsa Sridhar in Bengaluru; Editing by Christian Radnedge)
