Having moved to the States at the age of 14, Harrison was selected as the number one overall pick in the 2016 MLS SuperDraft by Chicago Fire, then traded to New York City where he linked up with Vieira.
The head coach was a big admirer of the winger’s intelligence on the pitch.
“His football brain is fantastic,” said the Arsenal legend, who had an open-door policy, so Harrison felt able to pester his boss for answers.
At Leeds, it’s somewhat different.
It’s not that Bielsa feels any less fond of his players, but he does like to keep a distance between himself and the members of his squad.
The upshot for Harrison, in this starkly contrasting working relationship, is that he has to think for himself when it comes to the requirements of his head coach.
“When you work with [Bielsa], if you’re smart about it you can figure out what he wants without having to ask,” said the loanee from Manchester City.
“What I had before, when I was working with Patrick in New York, I was always going to him and asking and asking, that’s how we built an understanding.
“But with Marcelo it’s not like that. He keeps a distance, he doesn’t like to build too close a relationship with his players.
“For me, it took me by surprise at first. Once you get past that, not relying on going to him and asking all the time, you start to work things out yourself as a player and really build an understanding without having too much communication.
“That’s something I’ve established, how to do what he wants without always having to ask.”
Bielsa’s door is not shut to his players, they do get regular input from the boss and he uses his staff to relay information to them, having analysed performances.
“We always have individual meetings and those help to build that understanding as well,” said Harrison, who has overcome his surprise at the arm’s-length management approach to thrive under the Argentine.
There was a strong feeling at Leeds in the summer that Bielsa could get a lot more out of the 22-year-old in their second season together at Elland Road and that is exactly what has happened.
Harrison has improved on a vast number of metrics upon which a player’s contribution to a team can be judged.
And he has become a mainstay, starting all 38 of Leeds’ Championship fixtures this season, having not missed any of their final 24 2018/19 league games.
“The last two years have been a great experience, working with him, I’ve learned a lot and I’m glad to have played so much,” he said.
“I’m trying to catch up to Klichy but it doesn’t look like he’s slowing down any time soon.”
So with Leeds holding an option to buy the winger from City at the end of his loan, there’s little reason for Harrison to cast his eye elsewhere, once this season is done and dusted.
Particularly if it ends the way he wants it to.
“It’s been great for my development,” he said.
“It’s been a great experience, the lads have been great, working with the coaching staff I’ve learned a lot.
“There’s no reason why I should say no I don’t want to be here next season.
“Hopefully if it’s in the Premier League, even better. Fingers crossed that happens.”