Krul will have the injury assessed by Unitedâ€™s medical team before any decision is taken over his availability for next Mondayâ€™s Premier League trip to Everton.
â€śSteve was at Newcastle when I was there â€“ and thatâ€™s quite a while ago,â€ť Ferdinand told the Evening Chronicle.
â€śHe is a very good keeper and, even though Tim Krul has been the first-choice for a while now, Harps wonâ€™t let anyone down if he is asked to come in.
â€śYou need a couple of top-class goalkeepers at your club, and in Krul and Harps Newcastle certainly have that.
â€śI think everyone is waiting to see exactly what the injury to Krul is, and how serious it might be, but it is a shame for the lad.
â€śHe has been in fantastic form for Newcastle over the last year
â€śI think he was probably goalkeeper of the season last year!â€ť