The Brazil international is spending his first season at the English club.
Casemiro singles out Marcus Rashford for praise after Manchester United’s 1-0 win over Wolves on Saturday.
Rashford came off the bench to score the match-winner for United as he continued his fantastic run of form.
The England international has scored in three consecutive matches for the Red Devils since returning from the World Cup.
Speaking to ESPN Brasil after the game, Casemiro hailed Rashford’s qualities.
“I’m gonna be very honest with you. I was really surprised with the player Rashford is,” the Brazil international said.
“In my opinion, especially knowing the player off the pitch, I can tell you that if he’s doing well, he can be one of the top five players in the world.
“He has an incredible way of hitting the ball, he’s got strength, he’s quick, is very clever playing. He was one of the players that really surprised me.
“Of course, when you play in a different league you already know the player, but when you’re in the same club every day.”
He added: “What a spectacular player. I’m enjoying so much playing with him. He gives us a lot of energy.
“I’m delighted to play with him. And I’m sure if he stays like this, with the conditions he has, he can easily be a top-five player because he’s exceptional.”