The 20 year old signed for United in January in a deal that could be worth up to £15 million (Dh86m) before being loaned back to Palace, who tackle Watford in the Championship play-off final.
Zaha netted both goals in the 2-0 semi-final win over Palace's fierce rivals Brighton and Hove Albion, and the Ivory Coast-born winger is eager to bid farewell on a winning note at Wembley Stadium.
"As I've said in many interviews before, it would mean the world to me to help get Palace promoted," he told the Palace website.
"That's all I wanted to do when I got my move, that was one of the main things I still wanted to achieve with Palace, and that's what I will try my best to accomplish before I go."
The Championship play-off final is reputed to offer the biggest financial prize in world football.
Today's match will be worth around £120m to the winning team, with earning potential in the Premier League set to sky-rocket as three lucrative new television deals kick in at the start of next season.
Palace have not played in the Premier League for eight years, while Watford last sampled life among the English elite in 2007.
Watford manager Gianfranco Zola, who enjoyed a glittering seven-year spell at Chelsea during his playing days, believes victory over Palace would represent one of his finest achievements in the game.
"I have been blessed to have enjoyed a fantastic career, with some very good moments, but to win this one would have it rated as one of the best because of everything you go through as a manager," said the 46-year-old Italian.
Watford have made extensive use of the loan market to bring in players from sister clubs Udinese and Granada, which are also owned by club owners the Pozzo family.
Palace's outspoken manager Ian Holloway has described the situation as "ludicrous", but he softened his tone in the build-up to this game, labelling Zola "a genius" for his work at the club.
Palace and Watford hope to follow Cardiff City and Hull City, who secured automatic promotion from the Championship earlier this month.
The three teams who go up will replace the relegated trio of Reading, Queens Park Rangers and FA Cup winners Wigan Athletic in next season's Premier League.
* Agence France-Presse
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