The Red Devils spent big to bring the goalkeeper to Old Trafford during the transfer window, although he has already made a number of errors.
The 20-year-old came under fire for his display against Manchester City in the Community Shield while he was also at fault for Shane Long's equaliser in their 2-1 win at West Brom.
De Gea faces a stern test against Bolton this weekend and Ferguson insists the youngster will come good once he knows more about the league.
"David made a couple of mistakes in his first games, which we didn't expect and nor did he," Ferguson told Inside United.
"It was unusual because his form at Atletico Madrid as an 18-year-old was sensational.
"There is no doubt we have a player of great potential. Our job at this club is to realise that potential and make sure he becomes a top goalkeeper.
"He'll do that once he gains experience and adapt to the physical nature of the league.
"It is a different game here compared to Spain - there are more crosses to deal with and there is more contact. Bit by bit, we will get there with him."