Ángel di María remained at Real Madrid for the 13-14 season due to Cristiano Ronaldo.
Di María was a key reason why they won their 10th Champions League trophy.
"The truth is that I have a great relationship with Cristiano Ronaldo and I stayed at Madrid last season thanks to him," di María told ESPN Radio.
"I left Madrid in the best possible way, by winning La Decima. In my farewell letter, I said exactly how I felt from the first day at the Bernabeu.
"I am grateful to Manchester United for meeting Madrid's demands. But I don't feel any extra pressure because I'm the most expensive player in the Premier League.
"The Premier League is more physical and about strength, whereas Spain was more about football. It's a very strong league, though. Van Gaal has told me to try to adapt as quickly as possible."