Diallo, born in Las Palmas to Senegalese parents, came through the academies of Las Palmas and Alavés before joining Borussia Dortmund in 2023, where he has spent the past season with the club's second team in Germany's fourth tier, making 28 appearances without scoring.
His stock has risen considerably at international level, however: the left-footed winger was part of the Spain squad that won this summer's European Under-19 Championship, scoring three goals in four appearances at the tournament. Several European clubs had shown interest, but Parma moved quickly to get ahead of the competition, with the deal aided by funds freed up from Bartosz Bereszyński's sale to Kasımpaşa.
The signing continues Parma's stated strategy of investing in young, developing talent as the club prepares for a season in which head coach Carlos Cuesta will look to build on last year's Serie A survival. Speaking to Sky from the club's pre-season retreat, Cuesta explained what convinced him to stay on at the club.
"The people I work with every day: the club, the players, the staff," he said, when asked what had persuaded him to remain in charge.
Asked about his ambitions for the coming campaign, Cuesta was measured.
"Our ambition is to improve: that can be a very broad word, but what we want to do is build on what we did last year. Improve our level of unity, compactness, clarity. We want to be an improved version of ourselves, to evolve," he said.
On his coaching philosophy, he added: "All of us coaches want to control the game, and what helps you most is having a higher line, having the ball. We're aware of what we want, but at the same time we know we need flexibility, to do what the game demands."
Cuesta pointed to preparation as central to his approach.
"The main point is preparation. You have to be competent, try to give solutions and allow players to develop. That has always been, I wouldn't say my obsession, but my main occupation. I always think about how to improve myself in order to help others improve," he said, before adding with a laugh when asked what this Parma side needed most: "Time to work — if it were up to me, I'd do four sessions a day."