But it now appears they've gained a new member of the Red Devils fanbase - the Pope.
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Pope Francis, who is 86 years old, met with a number of religious leaders from Manchester at the Vatican on Thursday, as well as Andy Burnham, the Mayor of Manchester.
But despite being there to pledge the region's commitment to tackling climate change, the politician also gifted the Pope a framed Man United shirt.
That's despite him being known to be a lifelong Everton supporter.
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Tweeting during the private meeting, Labour man Burnham said: "Good morning @LisandrMartinez. We are about to give your gift to the Holy Father!"
A photo posted later that day revealed the kit had defender Lisandro Martinez's name and number on the back, as well as a signed personal message from the 2022 World Cup winner.
With both household names being from Argentina, it's clear Martinez - who signed for Man United in the summer - wanted to send him a special message.
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"Your holiness, with much love, Licha," the Argentine wrote.
The central defender is ruled out until the end of the season following an operation on his broken metatarsal he sustained in the first leg of the Europa League quarter finals against Sevilla.
But whilst he focuses on his recovery, the rest of Erik ten Hag's side will be looking to bounce back on Thursday after conceding two late own goals in the first leg, which finished 2-2.