Roger Federer took a thinly-disguised jab at old rival - and potential Wimbledon semifinal opponent - Rafael Nadal on Thursday when he demanded play be speeded up at the Grand Slams.

Seven-time Wimbledon champion Federer believes the sport is in danger of losing support and its appeal to TV viewers by the length of time it takes some players to serve at the start of a point.

The Swiss star's comments came just hours after Lukas Rosol complained Nadal was constantly going beyond the 20 seconds allowed between points at the Grand Slams during his second-round loss to the Spaniard.

Federer said he had not seen Nadal's match against Rosol, but was keen to make an appeal to see action in general speeded up.

"I just think it's important that we, as players, play up to speed and don't exceed the time limit, because what I don't want is that we lose viewers because we play too slow," he said.

"I know you need to focus. You can do that in 10 seconds. Just can't be that we only see two points per minute. I just feel like we need to keep up the pace and obviously play according to the rules.

"The rules are there not to be broken, but of course you need to give leeway to tough rallies. I watched some matches, but they were playing so slow I was like, 'I really can't watch this.'"

Federer said he would not be surprised if tournaments installed a "shot clock" so that players, officials and fans could see how long some players take.

"I wouldn't be surprised if that were to happen all of a sudden because you only just need a couple of guys always doing it, and that's when it happens," said Federer.

"We have seen it in so many other sports, people who push it too much, and then you have to go the other extreme to counter that."

(China Daily 06/28/2014 page15)