Prior to Saturday, Ronaldo had looked a little jaded in recent weeks, and was struggling to make an impact on the pitch for the Red Devils.
And the attacker looked much better for it, as he netted a sublime hat-trick to fire the Red Devils to a 3-2 win.
But Ronaldo will face significantly less recovery time before United’s next game, with Atletico heading to Old Trafford on Tuesday tied 1-1 from the first leg in Spain.
Despite that, Rangnick insisted he has no concerns about Ronaldo’s freshness as he prepares to take on his old foes.
"I’m not worried that he has not been able to recover, he’s always been a person that looks after himself and his body,” the interim manager said in Monday’s pre-match press conference.
“He knows what to do. I’m not worried about that. If he can score another three goals, we will see. It’s not so easy to score three goals against this team [Atletico Madrid] at all.
“I think his overall performance [against Tottenham] was just good, if not very good, and this is what we hope to get from him again tomorrow night."
“I think he just showed what kind of professional player he is, and one what kind of level he can still play,” Rangnick added.
“For us it is important. Performances, like that, he showed he is still a very important player in this team and he can make the difference. Tomorrow, it would be good for us if he could show a similar performance to how he did against Tottenham.”
Learning from the first leg
Rangnick was asked about United’s approach to the second leg, and revealed two things he feels the Red Devils must execute if they’re to progress to the quarter-finals.
Firstly, the German wants to avoid a repeat of the first-leg showing, when United were sluggish out of possession and struggled to break Atletico down when they got the ball.
Rangnick also feels it’s hugely beneficial if his side can score first against Atletico, given how defensively compacted and organised the Spanish champions are.
"We saw in the first half in Madrid, what we shouldn’t do, how we should not play,” the 63-year-old told reporters. “This was a big topic for us yesterday and today when we spoke pre-match before tomorrow’s game.
“We have to know what it tactically takes, and the rest is all about energy. We were the team on Saturday against Spurs, who just wanted to win that game.”
"It’s very important [not to concede first]. Even more so against a team like Atletico, who don’t mind the other team having the ball.
“In their last four or five games they have played, they have had less than 50 percent possession of the ball. We are aware of that and we need to make sure, if possible, that we don’t concede at all. Yes, but it would definitely be important to score the first goal ourselves.”