Fergie said: "I watched the Scotland game and I knew straight away it was a bad one, the way the player came down on top of his ankle.
"It wasn't nice to see and it's a blow for Martin because he's a key player in terms of goals and at this time of the season there's too little time to recover from it.
"He and Cattermole are out so that is a blow for him particularly when you're in that dogfight at the bottom.
"It's not an easy position to be in - and the horrible part is that good teams go down in these situations.
"There have been great examples over the years. Nottingham Forest had Pearce, Keane, Nigel Clough, Des Walker, a team of internationals, and they went down. When you're in that area of the league it's very difficult to get a run of wins."