Fergie had plenty of time to address this lack of depth in midfield himself, but he didn't.
Yes, Moyes arguably could have done more to provide backup and competition for Carrick, but it's an accusation that could have been levelled at Fergie himself a season ago as well - the difference of course was that Carrick did not get injured last season, and United romped their way to the title.
While I agree Man utd clearly have problems with their midfield its weird to say that Fergie didn't address it. He bought Kagawa last season who didn't work out (or was injured I cannot remember) and knew how to use Jones, Carrick, Cleverly and Scholes to keep things working.
Moyes would have known from day 1 the midfield needed to be sorted out as Scholes wasn't going to come out of retirement for him and for some reason he thought spending a fortune on Fellani would be answer which seemed always doomed to fail.