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: "W e 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."
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.
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.