The pair had medicals with their respective new clubs on Friday and all that remained to complete over the weekend was paperwork, ahead of announcements that are anticipated at some point on Monday.
Gyabi is a highly-rated 18-year-old you joined Manchester City from Millwall and played a part in last season's Premier League 2 title triump for the young Citizens.
Leeds believe they are getting a player who will fight for first team squad involvement this season, although he is expected to feature for the Under 21s in the PL2 second tier. Gyabi will compete for a place in the midfield alongside the likes of Charlie Allen and Archie Gray, who is thought to have impressed during senior involvement in the first week of pre-season. Jack Jenkins will go out on loan but Lewis Bate, whose competition at first team level currently consists of Marc Roca, Mateusz Klich and Adam Forshaw, remains in the picture and will likely need minutes in the 21s too.
News of Gyabi's switch from the Etihad to Elland Road was somewhat of a bolt from the blue, coming as it did when the Phillips transfer was first revealed.
READ: The 'outstanding' 'Rolls-Royce' midfielder set to sign for Leeds United.A £5m fee for a player with no senior experience and relatively little game time at Under 23s level is sure to raise eyebrows as well as expectation, and a natural question - why are City content for him to leave?
Harry Brooks, a football coach and the founder of an agency that works with young academy players, trained with Gyabi in the summer of 2020 following an introduction by Borussia Dortmund prospect Jamie Bynoe-Gittens. Brooks says Gyabi's departure has few down sides for the mega-rich English champions.
"It doesn't really affect Man City when he goes because their remit is not to push people into the first team - of course that's the ideal, to have another Foden, but when you're a team whose expectation is win the league and the Champions League, to win it all, if you fail with £60m players on the pitch it's more excusable than if you fail playing with young players," Brooks told the YEP.
"The board, the fans are going to ask questions of you because they want to see the best of the best, so there isn't always that pathway. So for me it's not a question of Darko's abilities not allowing him to play for Man City, it's just that lack of pathway."
Leeds are able to point potential teenage signings in the direction of a pathway that has allowed Joe Gelhardt, Sam Greenwood, Crysencio Summerville and Leo Hjelde to enjoy first team exposure, although in many cases last season it was the small squad and its injury problems that led to promotions from the 23s. Marsch has been enthusiastic about the young talent at Thorp Arch, though, and did trust them in key moments last season. His selection shock on the final day of the season, starting Greenwood in midfield, was proof of that.
Another factor that has led to Leeds' capture of Gyabi is the sheer wealth possessed by Manchester City and the confidence it breeds. They know that, if it turns out they did let a gem slip from their grasp, they can just go and buy him back at a later date. Their successful pursuit of Leeds-born-and-bred lad Phillips is proof of that.
"If he goes elsewhere, like Leeds, and does really, really well, then Man City know they can be in the conversation to sign him up for £60m or £80m or whatever, because they don't mind that situation," said Brooks.
"It's probably going to happen with Gavin Bazunu, a top young goalkeeper going to Southampton. I'm pretty sure there's a buy-back clause in that particular deal but if there's not, if he goes really well and he proved himself to be a top tier goalkeeper, they'll just sign them back for quadruple the money because they've got the financial aspect to do that. So it works for them to let players go elsewhere."
Leeds are yet to confirm the identity of the new Under 21s coach who will be working with Gyabi but the club are confident they have their man lined up. His arrival will be one of a number of staffing changes this summer as Marsch completes a fuller backroom staff ahead of his first full season in charge.