The Red Devils have struggled to find their form under the 63-year-old at the start of the Premier League season, while the club also crashed out of the Capital One Cup at the hands of MK Dons.
However, Ferguson believes that United's problems stem from their lack of consistency in their back four, which has been affected by injuries.
"You can't get consistency or results until you get a regular back four. [Luke] Shaw and [Marcos] Rojo are young, Rafael is the only player with experience," Ferguson said at an event to promote his autobiography.
"Absolutely [Van Gaal is the right man]. No doubt in my mind he's the right man for the job."