Ferguson said the 27-year-old Danish stopper had suffered ligament damage and would be out for "at least four weeks, maybe five or six".
News of the injury means Spanish goalkeeper David De Gea is likely to line up against Chelsea in Sunday's Premier League clash at Stamford Bridge.
De Gea's form has come under the microscope recently following a shaky performance in the FA Cup fourth round defeat at Liverpool last weekend.
Source: AFP
Source: AFP