BRUNO FERNANDES was controversially sent off for a second Man Utd game in a row.
The Red Devils' captain received a second booking for a high boot against Porto.
United raced into a two-goal lead in Portugal's second city as Marcus Rashford and Rasmus Hojlund both took advantage of errors from goalkeeper Diogo Costa.
But Porto came roaring back with a strike from Pepe and an equaliser from summer Chelsea target Samu Omorodion - all before half time.
Omorodion then struck again to give the hosts the lead before the moment of madness involving Fernandes.
The United skipper - who used to play for Porto's fierce rivals Sporting - went in late challenging for a high ball against Nehuen Perez.
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The Argentine then fell to the ground clutching his face and the referee duly produced a second yellow card.
However, replays showed that Fernandes' boot did not make contact with the Argentine's head, with his leg only touching Perez's arm.
Fortunately however, Fernandes' predecessor as Man Utd captain was on hand to save boss Erik ten Hag from total embarrassment.
In stoppage time, when all hope appeared lost, substitute Harry Maguire popped up to head home an equaliser from a corner.
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The Porto game was the second in five days in which Fernandes has seen red - both in controversial circumstances.
On Sunday, he was sent off for a studs-up lunge on James Maddison during a 3-0 loss to Tottenham.
But he then had his red card rescinded after footage showed that he had slipped into the tackle.
That decision from the FA means he will be available for the match at Aston Villa on Sunday.
However, he will receive no such reprieve for tonight's red card as UEFA rules been a second booking can only be overturned in cases of mistaken identity.
That means he will miss United's next Europa League clash away to former boss Jose Mourinho's Fenerbahce.