Ronaldo has scored eight goals in 16 appearances against teams managed by Manchester City boss Pep GuardiolaManchester United manager Ole Gunnar Solskjaer has rejected the idea that Cristiano Ronaldo's signing has had a negative impact on his side.
Ronaldo, 36, returned to United in the summer when he joined from Juventus and has nine goals in 14 games this season.
"He's one of the best players that has ever walked on this planet," said Solskjaer.
"His impact so far has been absolutely immense. He scores goals, he works for his team. He's a top professional."
He added: "How people can say that's a negative, I can't see that one.
"We're really pleased he has started as well as he has."
Ronaldo scored United's opener in a 3-0 Premier League win at Tottenham last Sunday as the Old Trafford side bounced back from a 5-0 home thrashing by Liverpool.
The Portugal captain also scored two equalisers - the second in injury time at the end - in Tuesday's dramatic 2-2 Champions League group draw at Italian side Atalanta.
United host neighbours Manchester City on Saturday (1230 GMT) as they bid to put the "dark moment" of the Liverpool defeat behind them.
"We've moved on from that [Liverpool] one," added Solskjaer.
"Of course it's going to be in the history books, but we've had a good week.
"We've had good results away from home, difficult games, and the mindset is positive.
"We've got to go into this [Manchester City] game believing we can do good things. It's a local derby and everyone knows what's at stake."
United's win over Spurs was their first in five league games and they beat City 2-0 when the rivals last met in the Premier League in March at the Etihad.
Solskjaer has won four of his eight meetings against City boss Pep Guardiola in all competitions, which is the best rate of any manager to face the Spaniard at least five times.
"I'm not one to talk about what I've done. I've got great respect and admiration for what Pep has done," said the Norwegian.
"It's a special one and we've had a few good results against them. Let's hope that continues, but we don't take it for granted. We have to earn it.
"We've had some good games, tight games, and we need another performance."
City have not beaten United in the league in the last four meetings, with their last top-flight win against Solskjaer's side coming in April 2019.
"Congratulations to United for winning these duels against us, or some of them," said Guardiola, whose side were beaten by Crystal Palace in their most recent league outing.
"They have a lot of physicality, a lot of talent and people up front with the ability to win games by themselves.
"It's Manchester United - what should I say? Since the last century they have always been a good team, with the quality. But it is a new season, new games."
City were linked with a move for Ronaldo in the summer before he joined United and Guardiola added: "Normally I don't talk about players for other clubs.
"I am pretty sure Cristiano Ronaldo is happy at Manchester United and United are happy to have him. That's all."
