Despite Federer turning 40 next year, Kokkinakis suspects the ageless Swiss will reap the rewards from the likelihood of no grand slams being staged in 2020 while anti-vaccination proponent Novak Djokovic may suffer.

Federer was already going to miss a chunk of the season after undergoing knee surgery in February.

"He was going to take this time off and let his body rest and strengthen up anyway," Kokkinakis told AAP.

"So for him it pushes things back a little bit so for sure it helps him.

"I don't know how Rafa Nadal's knees are going and what-not or how he's feeling but it might help those two.

"I think the one it hurts maybe a little bit is Djokovic."

Serbian world No.1 Djokovic caused a stir last week when he said he was "opposed to vaccines" and "wouldn't want to be forced" to get one to travel when the tennis season resumes.

"That's his decision so that obviously won't help him tennis wise but, if he feels better doing that, go ahead," Kokkinakis said.

Trailing 20-times grand slam champion Federer by four on the men's all-time major titles leaderboard, and still three behind Nadal, Djokovic has indicated he may have a rethink about his anti-vaccine stance.

And he may need to, with Kokkinakis refusing to dismiss Federer as a grand slam force.

"The way he plays doesn't take a lot of physical toll on your body," Kokkinakis said.

"He makes it look so easy and he's really efficient with his movement.

"He has the ability to shorten points and play on his terms maybe a little more than Rafa and Novak.

"So he can kind of dictate the way points are going to go.

"I definitely still think he's probably better in this point in best-of-three (set tennis) and Wimbledon would probably be his best chance to get more slams but, who knows, you can't count him out.

"He's so good and has been for so long.

"A lot of times in the past when people thought he was done, he's come back.

"He was No.1 in the world at 36 so, if you're 36 and No.1 in the world, you can't doubt legends or champions like that.

"You've just got to respect them and see what they can do."

Australian Associated Press