Ivory Coast-born Zaha made more than 100 appearances in three years at Crystal Palace, progressing through the junior ranks at Selhurst Park.
Zaha signed for United in January 2013, but was then loaned back to the Eagles.
The 21-year-old was only able to muster two appearances for the Old Trafford outfit last term under then-boss David Moyes.
The England Under-21 graduate is deemed surplus to requirements under new manager Louis van Gaal, which paved the way for another stint at Palace.
Warnock was appointed Palace's new manager on Wednesday and moved quickly to rubbish suggestions Zaha has an attitude problem, backing him to realise his rich potential in south London.
"When you get the chance, you can't turn down Manchester United but there are so many big players there and sometimes you get a bit lost," said Warnock.
"He is still developing, Wilfried, and he has got so much talent. When you are a wide player, or a forward, you need to feel loved.
"I've heard it said about his attitude, but I've always thought his attitude has been spot on, so I'm looking forward to working with him."
- Sports & Recreation
- David Moyes