Sir Alex says De Gea was fully briefed about the rigours of English football prior to his arrival - and the warning immediately rang true when he made his league debut in August of last year.
"If you remember he played his first game away from home at West Brom and got a battering," recalled Sir Alex. "At the time I said referees will think he’s a young Spanish goalkeeper and he’s not tough and he didn’t get any protection at all.
"When we agreed to sign David, I had him at my house with Steeley and I got Eric in to explain how we played and what the game was like in England. He must’ve expected it to be different in that respect but I’m sure he was still surprised.
"Having to deal with it as a young goalkeeper was different. In the early days, it was a concern whether he was going to mature enough to handle that kind of play. But with the maturity we're seeing in him now, it doesn't bother him in the same way. He’s handling it. We don’t have any concerns about that.
"I don’t think you can prepare for it in training. Steeley does a lot of crossing with the three keepers but you can’t prepare for the real thing. We don’t want players crashing into one another in training!"
Sir Alex revealed he encouraged De Gea by pointing to how arguably United's greatest ever goalkeeper, Peter Schmeichel, had to adapt when he first came to England from his native Denmark.
"Yes, I spoke to David about Schmeichel and pointed out to him that in his first game at Wimbledon away from home he was screaming for protection from the referee.
"That mob [Wimbledon's players] were focusing right on him and battering into big Pete and he was screaming like a dying pig but he handled it.