Goals from Fred and Bruno Fernandes lifted the Red Devils into fifth place on the table but Ronaldo's histrionics somewhat took the shine off an impressive display from Erik Ten Hag's side.
Ronaldo, who was an unused substitute, headed straight for the tunnel just before the clock hit the 90th minute mark rather than wait and see out the win.
The 37-year-old also cast a frustrated figure when being substituted after 71 minutes in the goalless draw against Newcastle United on Sunday.
Ronaldo has only started two of Man United's opening ten league matches this season after failing to secure a move away at the start of the campaign.
While some have disapproved of the five-time Ballon D'or winner's latest conduct, others have given him the benefit of the doubt.
Speaking on BBC's match of the day programme, former England striker Gary Lineker said: "Cristiano Ronaldo: now we all know what a great player he's been and stuff like that, but walking off the pitch as a substitute with two minutes to go, before the game is finished, I'm sorry, but that's unacceptable. That's poor, isn't it?"
Pundit Micah Richards, a former Manchester City defender, agreed Ronaldo was out of order.
"It's so poor," said Richards. "For someone we've looked up to for so long, one of the greats of the game, to do that when your team are winning, making it about him, it's unacceptable."
Meanwhile, Ronaldo's former Portugal and Man United teammate Nani told Stats Perform News:"I don't know what happened in that moment.
"Maybe he had to go to the bathroom.
"Everyone knows he is a professional, very big professional."
"He works really hard to be on the field. Maybe [there can] probably be a little bit of frustration there on not being an option to play," Nani said.
"But this is his desire, to be on the field and play. But I think it's not a big deal because there is a reason probably."
