Vieira was Harrison's manager at New York City in the MLS and handed the now 25-year-old his senior debut in 2016.
The winger opted to take a different route to the professional game in the United States following his release from Manchester United as a youngster.
He eventually moved back to England to sister club Manchester City in 2018 after impressing for NYCFC under Vieira's watch.
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Harrison is now into his fourth season at Elland Road having spent the first three years of his spell in West Yorkshire on loan in LS11 before making his move permanent last summer.
His old boss Vieira - who Harrison has previously praised for his open-door policy and guidance while in New York - has been impressed by his career trajectory since moving back across the pond.
“I'm really pleased with how well he has been doing since leaving the MLS," Vieira said ahead of tonight's Premier League meeting between the Whites and Palace at Elland Road.
“He's a really talented young player who just needed to find the right place to play and to challenge himself because his work ethic is one of the best in the game.
“He is always wanting to improve his commitment to the game. It's fantastic and working with him in New York was really enjoyable.”
Asked if their was a member of the Palace squad comparable to Harrison, Vieira added: "In personality and their character and the way they are on the field, I would say Conor [Gallagher].
“They've [both] got this kind of energy. They love working for the team, they love the game, they love football. They’re always working hard for the team and these are the kinds of players with a big heart.”