Manchester United German Interim head coach Ralf Rangnick smiles on the pitch after the English Premier League football match between Manchester United and Tottenham Hotspur at Old Trafford in Manchester, north west England, on March 12, 2022. AFP
Rangnick's side host the Spanish champions in the second leg of their last-16 tie on Tuesday after a 1-1 draw in Madrid last month.
United are bidding to reach the Champions League quarter-finals for just the third time since the retirement in 2013 of Alex Ferguson, who won the trophy twice during his spell as manager of the club.
Ronaldo will be key to United's hopes of progressing after the Portugal striker silenced his critics in Saturday's 3-2 win over Tottenham.
The 37-year-old's treble came after a dismal run of one goal in 10 games, which raised questions about his future at Old Trafford, with suggestions he was unhappy with the club's direction under interim boss Rangnick.
Ronaldo has only 72 hours to recover from his exertions against Tottenham, but Rangnick is confident he will still be able to deliver a stand-out performance with so much at stake.
"Well, I'm not worried that he has not been able to recover," Rangnick said on Monday. "So far he's always been a person who looks quite a lot after himself, his body and he exactly knows what to do, so I'm not worried about that.
"If he can score another three goals, we will see. I mean, it's not so easy to score three goals against this team at all.
"I think his overall performance was just good, if not even very good and this is obviously what we hope to get from him again tomorrow night. But it's not just about Cristiano, it's about the whole team."
Ronaldo was often a thorn in the side of Atletico when he played for Real Madrid and his heroics against Tottenham will have given Diego Simeone's side more cause for concern.
Rangnick believes his star striker has underlined why he remains so feared by defenders across Europe.
"I just think he showed what kind of professional player he is, what kind of level he can still play," said the German.
"For us it's important with performances like the one that he showed, he's still a very important player in this team. He can make the difference."
United, struggling to finish in the top four of the Premier League, have not won the Champions League since 2008 but Rangnick is not looking that far ahead just yet.
"We want to try everything we possibly can and hopefully be in the last eight," he said. "But even if we do that, there are other good teams in the competition.
United midfielder Bruno Fernandes is available after testing negative for coronavirus having been ruled out on Saturday. Scott McTominay and Luke Shaw are also in contention after injuries.
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