Diafra Sakho looks to be out for the season
The Senegal international has been sidelined since he suffered a back injury in November which required surgery.
Sakho is now back in light training but West Ham medics say he will need a lengthy period of building up his fitness.
Head of medical and sports science Stijn Vandenbroucke said: “We must be mindful that Diaf is essentially at the start of his own personal pre-season training schedule.
Diafra Sakho has not played since November
“After undergoing back surgery and three months of rehab, a player needs time to reach sufficient fitness levels before we can contemplate making him available.”
Sakho missed the first three months of the season through injury and managed just two appearances – and one goal in the 1-1 draw at Manchester United – before succumbing to the back problem.
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The Hammers were hit with a triple injury blow during the 3-2 defeat by Leicester last weekend, with midfielder Pedro Obiang ruled out for the season with an ankle injury.
Defender Winston Reid will be out for five weeks after picking up a calf problem and winger Michail Antonio was forced to withdraw from the England squad with a hamstring injury which will sideline him for three to four weeks.