The final will be played at City's Joie Stadium rather than a Premier League ground, a scheduling outcome Fletcher publicly regretted, noting United had offered Old Trafford as a venue.
"We tried, because we really wanted a big stadium, and Old Trafford would have been an amazing occasion for the players, for everyone. Obviously we're disappointed, because I think part of this competition is about playing in these big venues. This competition has a special history. Players who have gone on and won Premier Leagues still talk about how amazing it was to win with their youth team and their friends."
On Gabriel himself, Fletcher, speaking with the Manchester Evening News, was unequivocal.
"JJ's an amazing talent and his enthusiasm for football, the enthusiasm that he brings to the pitch every day to learn, to want to play, to be on the ball — he's been a pleasure to work with. He's a fantastic kid. I think we have to remember he's a kid. And also that he's been part of a really good team, and the players have helped him as well."
Gabriel has scored 21 goals in the U18 Premier League this season, was named U18 Player of the Season on Tuesday and became the youngest scorer in United's FA Youth Cup history earlier this campaign. Fletcher is careful to keep the credit shared.
"JJ has scored the goals, and goals always get the limelight. He's an amazing talent with a major future and somebody I've enjoyed working with immensely. The team has given him the ball into those positions to score goals."
He praised Gabriel's character as much as his ability.
"He's desperate to do better, to improve, to learn. He takes constructive criticism fantastically, and I've got a great relationship with him. What a season he's had, and I'm excited for his future more than anyone."
On the question of whether Gabriel could feature in United's pre-season tour this summer — something widely reported as under consideration internally — Fletcher was deliberately measured.
"I don't know really. I think it's something that people above me will decide. All our players are capable of going on pre-season, not just JJ. It'll just depend on who's selected, what that looks like and what he needs for his next step."
He spoke carefully about the risk of accelerating a player's development beyond what they are ready to absorb.
"Once you get thrown in there, then you're judged very, very quickly, rightly or wrongly. It's important that we do right by his development. Getting variation in your development is really important. We want him to go up there and thrive, so we need to get him in the position to do that — and even if he doesn't, that's not the end of the world either."
The final against City at the Joie Stadium is Thursday evening.