West Ham has confirmed that midfielder Kieron Dyer fractured both major bones in his lower leg in a League Cup match at Bristol Rovers.
Dyer was hurt during a challenge by Rovers defender Joe Jacobson in the first minute of Tuesday's 2-1 win at Memorial Stadium.
West Ham said Wednesday that it was unclear when the 28-year-old Dyer, who only joined from Newcastle two weeks ago, would be able to return to action.
The club added that more detail would be available once Dyer had undergone his first round of surgery on the fibia and tibia of his right leg.
Dyer is the latest of West Ham's new signings to get injured. Fredrik Ljungberg, Julien Faubert and Scott Parker have all been on the sidelines since joining after last season, with Parker and Faubert yet to play for the club.
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