Federer ended a five-year wait for an 18th major title at Melbourne Park last year, beating old foe Rafael Nadal in an epic final.
Djokovic has not undergone surgery, but the decision to play in Melbourne was left until the eve of the tournament.
That is giving Djokovic some hope.
"If I'm not feeling good, probably I will not be here", Nadal said after his error-filled loss to Richard Gasquet in an exhibition this week. I don't know how it's going to behave.
Grand slam success is seen as a matter of when, not if, for Zverev but the ageless Federer stands ready to thwart another youth-led insurrection. "Who would predict that after his six months of absence, so. everything is possible really".
However, 16-time Grand Slam Champion is positive ahead of the Australian Open and is rearing to go and is motivated ahead of the tournament.
Off the court, the 30-year-old Serbian said he enjoyed a closer-to-normal family life off the court, including being there when his wife, Jelena, gave birth to their second child - a daughter Tara in September.
"So let's see. There's not much more I can do".
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"It's not entirely different, but at the beginning even those small tweaks and changes have made a lot of difference mentally", he said.
"I feel that I had a good week-and-a-half of practices".
It's very hard to go against Roger Federer, but if I was to pick someone who I think is going to have a big Slam this year, then I would say Juan Martin del Potro. "They spent a lot of hours analyzing my serve". Her career at Grand Slams looks like a "nearly" storyline - making the finals of the French Open in 2014 and 2017; semifinals at Wimbledon in 2014 and the US Open in 2015.
Ironically Djokovic was replaced by Andy Murray at Mubadala.
In recent months, meanwhile, ATP Finals victor Grigor Dimitrov and Zverev have moved up to No. 3 and No. 4 in the rankings, respectively, and are growing in confidence that they're on the cusp of Grand Slam breakthroughs. He's had the best preparation in many ways and the conditions here in Melbourne are pretty similar to how they were previous year, which was ideal for him.
"I've showed on multiple occasions over the year that I can play and beat the best guys in the world", Zverev said. I always wanted to be a top-five player.
Struggling star Eugenie Bouchard won her first match of the year Thursday, posting a 6-2, 6-0 defeat of Australian teen Destanee Aiava at the Kooyong Classic in Melbourne. Wawrinka hasn't played since the first round of Wimbledon at the start of July, while Raonic's comeback last week wasn't almost good enough, facing 10 break points in defeat in his first match back against youngster Alex de Minaur. "But I feel good", Nadal told the reporters ahead of the tournament.
"I love this sport, I really do". The Spaniard is hoping to be at his best for the tournament and wants to keep all expectations aside when he takes on Estrella Burgos in the first round.