Andy Mitten, editor of Manchester United website United We Stand, said the FA Cup win was “completely unexpected” and that the club “still have a lot of issues to sort out”.
Following Saturday's surprising win over defending champions and rivals Manchester City, there was a shift in the mood around manager Erik ten Hag's standing at the club and the team's performance.
But Mitten believes there is still plenty of work to be done this summer to make “significant” improvements before the start of the new campaign.
“It's a fantastic day in Manchester United's modern history because it was totally unexpected,” Mitten told BBC Radio 5 Live Breakfast, “and it's also a day to watch European football after a very disappointing league season.”
“Yes, we had injuries, but even with our strongest players we didn't play convincingly.
“It's been a really frustrating season but it's good to finish it on a high at Wembley.
“The game plan worked really well but the fans were really nervous with 10 minutes to go. A lot of guys did well, especially our defence who have been devastated by injuries.”
“This win gives confidence to the players and the club so the outlook is much brighter.”
United finished eighth in the Premier League, missing out on European qualification, and finished bottom of their Champions League group.
“There's still a lot of work to be done,” Mitton said. “We're not going to win the league next season – and I don't think the fans expect that – but we have to be significantly better than we were this season.”
“It was chaotic when he arrived but every manager will say that. I think he still has a lot to sort out and some of the players are still undecided about him.”
“He wants to stay but I'm not sure if he will. I wish he had a bit more charisma!”
