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 has subsequently been dropped by Manchester United manager Erik Ten Hag for this weekend's Premier League clash against Chelsea at Stamford Bridge.
Ronaldo responded to the incident on his official Instagram account, insisting his attitude has not changed.
"As I've always done throughout my career, I try to live and play respectfully towards my colleagues, my adversaries and my coaches," Ronaldo wrote. "That hasn't changed. I haven't changed.
"I'm the same person and the same professional that I've been for the last 20 years playing elite football, and respect has always played a very important role in my decision-making process.
"I started very young, the older and most experienced players' examples were always very important to me. Therefore, later on, I've always tried to set the example myself for the youngsters that grew in all the teams that I've represented.
"Unfortunately, that's not always possible and sometimes the heat of the moment gets the best of us.
"Right now, I just feel that I have to keep working hard in Carrington, support my team-mates and be ready for everything in any given game.
"Giving in to the pressure is not an option. It never was. This is Manchester United and united we must stand. Soon we'll be together again."
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.
