Ralf Rangnick was blown away by Cristiano Ronaldo's two-goal performance in Manchester United's win over Arsenal on Thursday night.
The German was in the stands at Old Trafford ahead of his debut in the dugout this weekend.
It offered him the chance to see his new squad up close and personal, with Ronaldo leaving a lasting impact.
The Portuguese star returned to Manchester in the summer and has continued to come up with big goals.
The 36-year-old has long been praised for how he looks after himself physically, which has allowed to him to continue playing at the top level.
Ronaldo scored United's second and decisive third goal, which came from the spot in front of the Stretford End.
Rangnick claimed he has "never seen a player" in such condition at Ronaldo's age, which bodes well for the remainder of the season.
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The German said: "You always have to adapt your style to the players you have available, not vice versa. I have never seen a player at Cristiano's age so physically fit.
"What I saw from him yesterday, he's more than willing to do what it takes to help the team."
Ronaldo has adapted his game as time's gone on which has seen him evolve from a winger to a prolific No 9.
He has rarely been asked to take on defensive duties or work off the ball however - something Rangnick's philosophy is renowned for.
That has caused debate over Ronaldo's suitability for the German, but there appears to be no concerns from his side.
United's squad are poised to take on new ideas with Rangnick inspiring current Premier League coaches Thomas Tuchel and Jurgen Klopp.
Their teams, Chelsea and Liverpool, are currently well clear of the Red Devils but Rangnick is confident they can challenge despite conceding they are someway off.
He added: "The squad is definitely good enough to compete in the top fight. The top three are stable, they have top coaches, if you look at the way they control games, we have to try do the same."
The German also said: "The players have to buy into the idea of how we should play in the future.
"It has to happen step by step, not in one or two sessions, but I'm more than happy with the quality of players we have here."
Rangnick will have to work without the assistance of Michael Carrick, who announced his departure following the Arsenal win.
Carrick had been part of Solskjaer's coaching staff and took over for a three-game period after the Norwegian's dismissal.
The German was keen to keep the 40-year-old at Old Trafford and made attempts to sway his decision, but had to accept defeat.
He claimed: "I got to know this two days ago. Had a private conversation with him for more than an hour. I tried to persuade him to stay on board but in the end I had to accept his decision."