LONDON (REUTERS) - The tennis balls becoming heavier during play on the grass at the All England Club is to be blamed for the slower game at the Wimbledon and not the playing surface, third seed Rafa Nadal said on Saturday (July 6).

Many players have complained about the game's slower speed at the Grand Slam this year, with Roger Federer saying Wimbledon "has not been the fastest" while Caroline Wozniacki complained about the grass on Court Two after her third-round exit.

Nadal, who beat Jo-Wilfried Tsonga 6-2 6-3 6-2 to march into the fourth round, did not have any issues with the surface but pointed out that the humidity on court was a factor.

"It's not the surface. It's the balls that are a little bit heavier. Sometimes it's normal because we play on grass," Nadal told reporters.

"The balls get some humidity, that's part of the game. It's true that sometimes the balls are heavier than the other events here.

"I think the balls are always heavy here in Wimbledon, no? That's something that, in my opinion, is the main thing that makes sometimes the game little bit slower."

When pressed about the surface, Nadal said he did not find any difference.

"Honestly, the surface for me is the same as always," the Spaniard added. "I have been playing here since 2003, I don't see a difference on the surface.

"When I hear people saying, 'That's very slow, faster, slower than ever...' Every time I am hearing the same. Sometimes the feelings of the players are not exactly the same.

"For a player who is playing very well, they can feel the thing is perfect. For a player that is not playing that well, they feel slower or too fast because it's difficult to find the timing out there."

Nadal will play either Portugal's Joao Sousa or Britain's Dan Evans in the fourth round next week.