The Ecuador international injured his knee and ankle during the club's 2-2 draw with Astra Girugiu and he now appears set to miss the start of the Premier League season.
West Ham has been dealt a blow in the build up to the Premier League season after Enner Valencia suffered a "significant" injury during Thursday's Europa League clash with Astra Giurgiu.
The Ecuador international 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.