Lopez, who coached Barcelona B between 2015 and 2018, first worked with Cucurella when Alex Grimaldo held down the left-back spot in the first team picture.
"He caught my eye from the very first moment. I came in as Barça B coach in the summer of 2015 and the left-back was Grimaldo. He was brilliant, but as I saw the club wasn't fully backing him for promotion, I started putting my faith in a kid who was shining in the Juvenil A. That was Marc, three years younger than Grimaldo."
Cucurella eventually found himself competing with a third talented full-back, Juan Miranda, before Jordi Alba's dominance at left-back squeezed all three out of Barcelona's plans.
"It's rare to have three young players of that level competing for one position at the same time. I'd sometimes play Grimaldo or Miranda at full-back and Cucu on the wing so all three could feature. I kept faith in Cucurella even as I saw the club leaning more towards Miranda, and then there was the wall Jordi Alba created in the first team. That's why Cucu ended up leaving too."
Lopez insists the decision not to promote him was a mistake, telling AS: "They kept buying left-backs as backups for Alba, who was undroppable. They paid for Junior Firpo and Lucas Digne when they had incredible talents in the B team. Barça get it right often trusting academy kids, but they got this one wrong, and those boys had to make their way elsewhere."
He gave Cucurella his senior debut against Hospitalet in 2016 at just 18.
"Marc had brutal physical ability and was technically excellent. He was almost too good to be a left-back. I could easily have played him in central midfield. He never lost the ball, had an exquisite first touch and total command of the situation."
Asked whether Cucurella's move to Real Madrid bothered him personally, Lopez was unequivocal. "Above everything, I feel happy that things are going well for him. Marc thinks about his future, and if he's decided this is best for him, that's fantastic. He's joining a huge club and I wish him every success."
On how Cucurella might fit alongside Vinicius Junior on the left side, Lopez expects Jose Mourinho to find the right balance.
"I'm sure Mourinho already has a plan to balance the side. Cucurella is smart and will adapt to anything. If Vini drifts wide, Cucurella knows how to tuck inside and link with midfield, something he does very well. He has the capacity to adapt to whatever's needed, and Mourinho will get the best out of him."
Lopez has no doubts the transition will be smooth: "Given his character, he won't have any problems. He's a humble lad who never forgets where he came from, and his transfer is going to be a huge success."