Manager Sir Alex Ferguson has admitted that he "didn't expect" new goalkeeper David de Gea to make mistakes so early into his Manchester United career.

The 20-year-old has produced a handful of errors in his opening four matches for the Red Devils, but Ferguson has backed the £18m signing to be a success at Old Trafford.

"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."

De Gea has kept one clean sheet in three Premier League matches so far.