The 21-year-old winger will join the Welsh outfit until the end of the season after Old Trafford officials granted his wish for a move.
Zaha stormed out of training last week after he was told that the champions would not sanction a temporary move, but Ashley Young's return to fitness and the imminent arrival of Juan Mata has seen Old Trafford officials reconsider.
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Sources at United have indicated that there are concerns over the youngster's attitude and development since his arrival at the club, with relations having been left strained after the altercation over a loan move being vetoed last week.
However, with Young having recovered from a shoulder injury and Mata expected to complete his 37 million pound deal with United on Thursday, United officials are satisfied that the squad has enough strength in midfield to allow Zaha a move until the end of the season.
The England U-21 international has not yet undergone a medical ahead of the move to South Wales, but went for a scan on a toe injury at Manchester's private Bridgewater Hospital on Wednesday.
Newcastle had previously been in pole position to land Zaha but new Cardiff manager Ole Gunnar Solskjaer has looked to use his United connections to secure one of the brightest young talents in English soccer.
Moyes has gone on record to suggest that a loan deal would suit Zaha’s development and benefit United in the long run.
Zaha has made just four senior appearances for the Premier League champions, and his only two league appearances have been as a substitute.