Once viewed as the long term successor to Zlatan Ibrahimovic, the Swedish striker returned to form after being loaned out to Celtic during the 2014-2015 season and has continued his strong play since signing with Celta Vigo in 2015.
His time with City was plagued by illness and injury, leading to his eventual departure but despite only making a single appearance with the Sky Blues in a League Cup tie, Guidetti remains loyal to his former club.
"I played in England and lived in Manchester for six years, so I follow both of the teams there," Guidetti said in an interview on UEFA's official website.
"United are a very good team. Obviously they've got a good manager, a fantastic stadium, and they're one of the favourites to win the Europa League.
"But as they say, Manchester is blue, and that's how it will be when we visit there as well, because we are Celta Vigo and we will try to keep the city blue."
Guidetti's former international teammate Ibrahimovic will miss the game after picking up a knee injury during the quarter-finals of the tournament against Anderlecht, with the 24 year-old expressing his regret at not being able to face the charismatic striker.
"Of course, it's very sad what happened to Zlatan. With how much he has meant for Swedish football, he has also earned the right to play in the final at the Friends Arena," he added.
"Unfortunately he is unlikely to be able to play, so I wish him a speedy recovery."