West Ham striker Enner Valencia suffered an apparently "significant" injury to his right knee and right ankle in the Europa League clash with Astra Giurgiu, the club have announced.
The Ecuador forward was starting his first game since returning from the Copa America, but was stretchered off with a potentially serious knee injury before half-time.
Manager Slaven Bilic said after the game he feared the injury was serious, and an update from West Ham on Valencia's health indicated he was right to be worried.
Valencia could face a long absence from first-team availability, but West Ham will wait for him to visit a specialist at the start of next week before forecasting how much of the season he stands to miss.
The club said in a statement on their website: "Enner Valencia sustained what initially appears to be a significant injury to his right knee and right ankle during Thursday's UEFA Europa League third qualifying round first leg tie with Astra Giurgiu.
"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."
