Roger Federer believes his Wimbledon quarter-final opponent Kei Nishikori is ready to challenge for grand slams.

The Japanese, who reached the US Open final in 2014, has moved seamlessly into the last eight for the second year running, but faces the toughest test of all against Federer on Centre Court.

Nishikori is at least fit and firing, having often struggled with injuries in key matches in the past, and will have to be at his very best to stop the eight-time champion racking up a century of wins at SW19.

Federer, who has barely broken sweat on his way to the quarters, is wary, though.

"I think it's going to be tough," he said. "He's getting into quarters with a lot of energy.

"I remember some of the slams recently he arrived into the later stages of slams with maybe some tough matches going into it. So far it's been really easy for him.

"I think he's ready. I'm a big fan of his game. I think he's got one of the best backhands in the game that we have right now.

"I know it's not going to be easy, but I will enjoy for sure."

That is the standout tie of the quarter-finals of a men's draw that has again highlighted just how far ahead Federer, Novak Djokovic and Rafael Nadal are from the rest.

All three men have dropped just one set so far and will be big favourites to progress.

Nadal is up against 2017 semi-finalist Sam Querrey, who is hoping to blow the Spaniard away with his serve.

"Novak is playing so well in grand slams," he said. "It is so tough to beat him in the best of five and especially here on grass.

"I think when he's playing his best tennis, he is the world number one and is probably the best.

"Even for Roger, it will probably be the toughest challenge for him."

Quarter-final debutants Robert Bautista Agut and Guido Pella face off in the remaining tie.