West Ham midfielder Jack Collison has been ruled out for six to seven weeks with a dislocated kneecap, the club have confirmed.
Collison hurt his right knee in the second half of the 1-0 win against Wigan last Wednesday.
The 20-year-old underwent an arthroscopy on Tuesday to assess and deal with the injury and is reported to be recovering well.
It is the second serious injury blow the Hammers have suffered this week.
On Tuesday fellow midfielder Valon Behrami was ruled out for six months with an anterior cruciate ligament injury in his left knee.
The 23-year-old was injured during the defeat against Manchester City at the start of the month and underwent keyhole surgery in Italy.
West Ham are currently seventh in the Barclays Premier League and face bottom side West Brom at Upton Park on Monday.
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