Pereira has struggled for first-team appearances since moving to Old Trafford in 2014, and despite Jose Mourinho wanting to keep him at Old Trafford 12 months ago, the playmaker opted to make the temporary switch to the Mestalla Stadium.
However, Pereira went on to make 18 starts and 11 substitute appearances in all competitions, and the Brazilian has revealed that he now has a strong relationship with his manager.
The 22-year-old told Sky Sports News: "It was very difficult for me to take that decision. Like Mourinho is one of the best coaches in the world, and he tells you to stay, and if you go against it you've only got things to lose in your head really.
"I was nervous about that, but it came out well. We had a great year in Valencia, and I am a better player, and this season he has a better Andreas than he could have had last year.
"He hasn't told me, but I think he will see this in games. I have a very good relationship with him, he is very good with me, very honest."
Mourinho handed a start to Pereira as United registered a 2-1 victory over Leicester City in the Premier League last week.