However, that has not stopped Guidetti - now at Celta - from trying to get under the skin of the United fans ahead of the semi-final clash with Jose Mourinho's men.
"I played in England and lived in Manchester for six years, so I follow both of the teams there," he told 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.
Celta suffer third straight Liga defeat and fifth in six top-flight games, at home to Athletic. Next up ... Manchester United! #UEL pic.twitter.com/Eq1xNTr1Hn — UEFA Europa League (@EuropaLeague) April 30, 2017
"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 countryman Zlatan Ibrahimovic will miss the tie due to a serious knee sustained against Anderlecht in the quarter-finals.
And Guidetti expressed his regret at not being able to face the Sweden great.
"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."