West Ham have been dealt a blow just a week before the start of the Premier League season after Enner Valencia suffered a "significant" injury in Thursday's UEFA Europa League clash with Astra Giurgiu.
The Ecuador striker was carried off on a stretcher after damaging his right knee and ankle during the first half of the 2-2 third qualifying round first leg draw against the Romanian side at Upton Park.
West Ham confirmed on Friday that the 25-year-old's scan results were not positive, but the London club are not yet aware how long he will be ruled out for.
A statement on the club's official website said: "Enner Valencia sustained what initially appears to be a significant injury to his right knee and right ankle.
"The Ecuador forward will see a specialist consultant at a clinic in central London on Monday morning and an update will be provided following that meeting.
"It is too early to put a timescale on how long Enner's recovery and rehabilitation period may be."
West Ham also lost Joey O'Brien to injury during Thursday's clash, in which they were 2-0 up before being pegged back after James Collins was sent off.
With Andy Carroll still sidelined, West Ham are facing with a shortage of strikers heading into the new campaign.