I think our left-back position could make a solid argument that would dispute the factual nature of such a claim... but I digress.
Fergie is and was always going to play the majority of games with 2 people in the centre of the pitch... that's just how he operates, and there's nothing really to suggest he would change his way of thinking.
So, for two midfield spots you have Carrick, Scholes, Giggs, Anderson, Cleverly, and a seemingly on course to return Fletcher... with Powell and possibly Kagawa also in the frame. That's 6-8 players for 2 places... you can argue about personel, but in terms of numbers, that's pretty well stocked. Yes, Clev and Ando have poor injury records, but they're part of our squad... and so we must treat them as if they are going to remain fit and contribute to the team. If they're not, then we should be selling them...
If Fergie thinks Clev/Ando can only play in 10 games this season, I doubt he'd be keeping him around, and nor should we. We can't treat them as if he's going to spend the season injured, I mean, what if he manages to remain fit for the whole season? and what if Ando did too? Wouldn't a new CM hamper their development in that scenario? Again, people will say "but that's not going to happen because they're crocks" ... but if they're part of our squad, we shouldn't be treating them that way.
It's a different issue if people think we need a central midfielder to improve our current ability (i.e, a better player then Carrick, Clev, Ando et al) in the centre.