While coaching kids in New York, Roger Federer revealed that the player he struggled against the most was fellow Big Three member Rafael Nadal.

20-time Grand Slam champion Federer faced many of the strongest players during his professional career.

These rivalries included the likes of Andy Roddick, Lleyton Hewitt, and Andy Murray, as well as the only player from the Big Three who is currently playing, Novak Djokovic.

However, whilst spending some time working with kids in the US, Federer was asked which player he found to be the most difficult to play against, to which he responded with Nadal,

"I struggled against Rafa the most. Yeah, just bc of his topspin and lefty, you know," he said.

In order to reinforce his point, he then asked the kid,

"Do you like playing against lefties?" to which they replied with a definitive "No", prompting Federer to jokingly respond again with "There you go."

The 41-year-old faced the Spaniard 40 times during his professional career, which is ten less matches than the Swiss has had with Djokovic.

From 2006 to 2008, Federer and Nadal played in every French Open and Wimbledon final, with the 2008 SW19 final often considered one of the greatest tennis matches in history. The pair also held the top two places on the ATP rankings from July 2005 to August 2009.

The two men's hugely impressive achievements in the sport demonstrate just how difficult both of them were to play. When faced with each other therefore, Federer is right to admit that he struggled against the 37-year-old.

One of the clearest examples of how much they pushed each other in their careers is shown in the final of the 2006 Rome Masters. Their match lasted five hours, with Nadal eventually winning on a fifth-set tiebreak after saving two match points.

In the overall head-to-head, Federer trails 16-24, although he leads 3-1 on grass and 11-9 on hard courts, thus indicating Nadal's utter dominance on clay, where he leads 14-2.