West Ham will be without Enner Valencia for up to 12 weeks and the club admit there remains a possibility he may yet require an operation.
The 25-year-old forward had given the Hammers the lead before being carried off on a stretcher in the 2-2 Europa League third qualifying round draw with Astra Giurgiu last week.
The club said on Friday Valencia had suffered what "appears to be a significant injury to his right knee and right ankle" and refused to put a time frame on his return ahead of a meeting with a consultant on Monday.
Following that meeting Stijn Vandenbroucke, the club's head of medical and sports science, confirmed the Ecuador international could miss up to three months and – despite Valencia suggesting that he does not need surgery – Vandenbroucke did not rule out the possibility completely.
"Enner visited the consultant on Monday morning, when we discussed the results of the scans he underwent on the injury last Friday," he told the club's official website.
"The outcome is that there is now a very small chance that he will need an operation and that we instead hope to treat the injury to his fibula using conservative treatment, which we hope to start in three weeks.
"We will know for sure whether or not Enner will need an operation next week, but if everything goes to plan we hope that he will be available for selection again within 10 to 12 weeks.
"Enner will spend the next three weeks in a walking boot and using crutches, after which we will start his rehabilitation."
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Despite Vandenbroucke's comments, Valencia took to Instagram to post a picture of himself from the Astra game and wrote that he does not need surgery.
"I would like to thank everyone for the support and the affection shown on this difficult moment. Thanks God, today I received great news as I won't need surgery, all the best!" he wrote.
With club-record signing Andy Carroll also out injured, Irons boss Slaven Bilic is still likely to add another striker to his squad before the transfer window closes.
He has Diafra Sakho, Mauro Zarate and Mobido Maiga to chose from for the return leg in Romania and their Barclays Premier League opener at Arsenal on Sunday.
A loan move for Atletico Madrid and Mexico forward Raul Jimenez has been widely reported, but the 24-year-old would require a work permit before making the move to Upton Park.
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