The 20-year-old has set the Championship alight this season after helping the Selhurst Park club climb into the promotion places.
It is understood, according to reports, that Zaha will be loaned back to Ian Holloway's side for the remainder of the season as Palace chase a return to the Premier League.
But the capture of Zaha is also set to signal the possible end of Nani's time at Old Trafford.
With Ryan Giggs on the verge of retirement, the arrival of Zaha will be a boost to the United squad.
However, the lack of service from the flanks this season has been a concern for United manager Sir Alex Ferguson as he attempts to wrest the Premier League title back from Manchester City and claim a third Champions League victory in his reign.
Ferguson was swift to counter, though, telling Manutd.com in an interview picked up by The Independent, that Nani would be going nowhere.
However, the signing of Zaha suggests Ferguson is looking for more from his wide men than he is currently getting.
Nani made his first appearance for United since Nov. 7 when he played in last week's FA Cup third-round replay win over West Ham United following a hamstring injury.
That injury could well have played a part in the Portugal international not enjoying the best of form before being forced onto the sidelines.
The reality, however, is Ferguson will be using the arrival of Zaha as a kick up the backside for all of his wide men, including Young and Valencia.
And has Ferguson forgiven Nani completely for the alleged bust up with reserve player David Petrucci in September, which was reported by the Daily Mail?
Much will depend on whether Nani can recover his form and fitness in the second half of the campaign to ensure his Old Trafford future ahead of both of his teammates.