Some press reports estimate that the injury could see him miss eight weeks - virtually the rest of the season - but the general consensus seems to be around the five-week mark.
Generally I would not regard the loss of Dyer for a period as a major blow to the team but, with Darren Ambrose also out injured and Lee Bowyer still banned in Europe, the timing could not have been worse.
Meanwhile, reserve team skipper Bradley Orr has been recalled from his loan spell at Burnley to provide extra cover in midfield.