Manchester United announced the deal via their Twitter account:
The Manchester United winger has found it difficult to break into the Red Devils' senior ranks since arriving at Old Trafford, despite Louis van Gaal's appointment over the summer.
Zaha left Selhurst Park in January 2013, spending the latter half of the 2012-13 season on loan with the Eagles before joining up with the Red Devils later that year.
However, the 2013-14 campaign didn't yield much fruit, and Zaha headed out on loan again in January 2014, spending five months with Cardiff City, unable to prevent the Welsh outfit escaping relegation.
Warnock spoke to talkSPORT on Thursday, confirming that a deal to bring Zaha back was nearing completion, and that more transfer activity is expected before Monday's deadline:
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. 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. We are looking really hard now and there are three, four, maybe even five needed before Monday.
The £59.7 million arrival of Angel Di Maria at Old Trafford has given Van Gaal more options in attack as the Dutchman looks to establish a new depth in class among his squad.
Sky Sports' Peter Hall hints that attitude issues are one reason Zaha hasn't made his step up in United's ranks thus far, and that Warnock's tutelage may not stand to benefit that side of his persona:
However, one thing guaranteed is that the trickster will have a better chance of Premier League playing time with Palace, a familiar setting that could coax some of the form that first put him on top-flight radars.
In 14 Premier League appearances—two for United, 12 for Cardiff City—Zaha has made one assist, according to Transfermarkt.
His last season with Palace tells a far more positive tale of six goals and 10 assists in 43 Championship outings, although England's top division is proving more difficult to crack.
United will hope to see their starlet return to Old Trafford next summer having rediscovered the magic touch displayed in previous years, with Warnock having overseen the player for a portion of his academy development.