Alli, in his first game since February 2023, was sent off 10 minutes after he was brought on during Como's 2-1 loss to AC Milan at the San Siro.
The former Tottenham star was shown a red card for his ugly challenge on Loftus-Cheek as he planted his studs on the back of the Milan man's calf.
The referee initially brandished a yellow card for Alli but it was upgraded to a red after he consulted the pitchside monitor.
Not even a desperate plea from former Tottenham teammate and Milan defender Kyle Walker was enough to persuade the referee to change his mind.
After the foul, Loftus-Cheek remained on the turf for some time.
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It lead some to ponder whether Alli's challenge left the Milan ace in some discomfort.
But in an Instagram post, Alli revealed a conversation with Loftus-Cheek that proved he was not hurt.
Instead, it was for a completely different reason.
"I stayed down coz (sic) I was blowing," Loftus-Cheek said.
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Alli replied alongside three laughing emojis: "Don't p*** me off."
Earlier in their exchange, Alli told Loftus-Cheek he 'just tried to clip ur (sic) heel'.
The foul took place just over 10 minutes after Loftus-Cheek came on in place of Rafael Leao as Milan looked to preserve their 2-1 lead.
It was also Loftus-Cheek's first appearance January 6 having been sidelined with a muscular issue.
As for Alli, it was his return to action after an absence that nearly spanned 750 days.
But he will have to wait at least one match before he can log his second given he will be suspended following the red card.
Speaking after the contest, Como boss Cesc Fabregas conceded Alli 'perhaps didn't deserve' to come on as he lamented the Englishman's 'grave mistake'.
"It was at that moment when Milan went 2-1 up and Sergi Roberto was meant to come on, but I'd prefer to give him another two weeks to train so he can be ready to start against Empoli," Fabregas said.
"Dele Alli is a player who can score goals, he perhaps didn't deserve this opportunity because he has only been working with us for two weeks and has a lot to improve.
"It is a grave mistake, one that we should not see from a player of his experience. It was a clear red card, there's nothing to be said about that, he left the team down to 10 men during a crucial moment when we were pushing for 2-2.
"That is the most negative thing about this evening, but we keep going."