Roger Federer was defeated in the US Open quarter finals by the Argentine Juan Martin del Potro, who will face Rafael Nadal in the semi-finals at Flushing Meadows in New York.

The Argentine 24th seed, beat Federer in four thrilling sets on Wednesday night.

Had Federer beaten del Potro, it would have set up a first clash between himself and his great rival Nadal at Flushing Meadows. It would also have given him an opportunity to regain world number one spot for the first time in since 2012.

However, despite his disappointment at not facing Nadal, Federer still has offered his opinion on the upcoming semi-final, and expressed his excitement for what should be a thrilling contest:

"I think it’s going to be an exciting match, you know, both are great shot makers. They have, you know, some of the best forehands in the game. They are both winners. They know how to get it done. I think it should be an exciting semi."

With an expert knowledge of both semi-finalists' game, Federer knows what fans should expect but did warn a lot could depend on the fitness of Del Potro.

"Rafa now is playing within himself a lot. I think he was very focused here, in practice and also in the matches. I assume we know what we’re going to get from him.

"Juan Martin, I hope he recovers, you know. It’s big for him now to have a day rest tomorrow, because again, it’s an emotional night and all that stuff.

"Rallies weren’t very long, so he did well to bounce back from his Thiem match, you know. That was nice for him. You know, I think it should be an exciting match. I’m sure the crowd’s going to get into it."

Regardless of the eventual winner, it will be a fascinating contest. The victor will also be considered the big favourite for the final with neither of the other two semi-finalists, Kevin Anderson and Pablo Carreno Busta, having reached a Grand Slam final before.