Meanwhile, Federer is hoping for an Australian Open hat-trick after winning in 2017 and 2018.
Djokovic won his third US Open in September to put him on 14 Grand Slams - three behind Nadal and six behind Federer.
What Murray wants to do after spending almost his entire life playing tennis is to have some fun, play five-a-side with his mates, and fit in some golf - which might have been his chosen sport, if his father, Willie, had had his way, rather than his mother, Judy, who steered him towards tennis. "Like, I get to the ball faster, and I'm not as sore", she said.
From the moment he won his first matches at Wimbledon as an 18-year-old in 2005 and picked up his first title in San Jose in 2006, Murray has lived his professional life in the spotlight, the great hope for tennis in Britain, a country starved of success for so long. "It just maybe looks that way".
"But I think it will all come down to, is it the body, is it the family, is it the mind, is it one morning when I wake up, how does it happen?"
Of all the tributes that have flooded in, it was the one from Wimbledon that said it best: "To Andy, whatever happens next, you've done more than you know". We like him. He's a good guy, Hall of Famer, legend.
Williams has a tough road to an eighth title, with world number one and French Open champion Simona Halep a potential quarter-final opponent followed by Osaka in the semi-finals if the seeds hold sway.
Murray faces a first-round clash Monday against in-form Spaniard Roberto Bautista Agut, seeded 22, who beat Djokovic on his was to winning the Qatar Open earlier this month.
"But I know that tennis is not forever".
" After so many years competing at the top level, to then feel you have a limitation that does not let you do what you want to do, it is a daily agony that makes you want to give up for your physical and mental health."
She disputed the bookies' assessment that Serena is red-hot favourite to lift the Australian Open trophy for an eighth time, taking her overall Grand Slam tally to 24 and equalling Court's mark. He can play well in fast courts. He will continue playing through the Australian Open, noting, "I can still play to a level, not a level I'm happy playing at".
"It's sad for me, but for all sport, because Andy is a very respected and likable guy around the locker room", Djokovic said. "That's always a good thought".
"But other than that, I feel like it's really individual, I think from person-to-person, how you react to different things".
Murray said he made the decision back in December while struggling through a pre-season training camp. Even if a lot of days you go on court when you have troubles or you go to the gym without having a real goal or without knowing why I am going there, because I don't see a benefit ... you keep going.
What few knew as her season drew to a close was that the indefatigable Dane had been diagnosed with rheumatoid arthritis, an auto-immune disease that can cause swelling and pain in the joints.
"Yeah, of course is very bad news", Nadal said.