West Ham striker Diafra Sakho appears unlikely to play again this 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 told the club website: "We must be mindful that Diaf is essentially at the start of his own personal pre-season training schedule.
"When players return from their off-season, they will go through four to five weeks of pre-season work to build up their strength and fitness and, 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 for selection in the Premier League.