New Manchester United manager Ralf Rangnick said he has never seen a player as physically fit as Cristiano Ronaldo following his two-goal display in the 3-2 win over Arsenal in the Premier League.

Rangnick was unveiled as United's interim manager at a news conference on Friday, with the German appointed until the end of the season following the sacking of Ole Gunnar Solskjaer.

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There have been questions raised over whether 36-year-old Ronaldo will fit into Rangnick's high-pressing style and the Portugal captain was dropped to the bench last weekend for the 1-1 draw at Chelsea.

But Rangnick, who was in attendance at Old Trafford on Thursday as caretaker boss Michael Carrick took charge for the final time, said he was impressed by Ronaldo's performance against Arsenal.

"You always have to adapt to the players you have available, not vice versa," Rangnick said. "Seeing Cristiano yesterday, 36 years old, an amazing top professional. From what I saw he is ready to do what it takes to help the team.

"At his age, I've never seen a player who is that physically fit."