The result heaps pressure on United boss Ole Gunnar Solskjaer, who called it his “darkest day” and said his side had hit “rock bottom”.
However, Ronaldo, who had a would-be consolation chalked off by VAR, took to social media and insisted the players take responsibility.
“Sometimes the result is not the one we fight for. Sometimes the score is not the one we want. And this is on us, only on us, because there’s no one else to blame,” Ronaldo wrote on Instagram.
“Our fans were, once again, amazing in their constant support. They deserve better than this, much better, and it’s up to us to deliver. The time is now!”