It all means the era of the "Big Four" is nearly over after a season in which Federer - who opens his title defence against Denis Istomin on Monday - rolled back the years on Rod Laver Arena to lift an emotional 20th Grand Slam.
Williams has reached the finals of the past two Grand Slam, and she looked relatively sharp at the Hopman Cup in Perth in the first week of January.
It has been suggested that a hip replacement would be beneficial for the three-time grand slam champion, but O'Donnell added: "Andy has tried really hard and explored every option that has any real possibility of being helpful". He's targeting retirement at Wimbledon.
"I hope it doesn't end with an injury", Federer said to of his own career.
"Now I know how to manage better if that happens again".
His great rival Nadal expressed his sadness at Murray's impending retirement but backed his decision as the right move for his mental health. 'We like him. He doesn't have many enemies, to be quite honest.
"It's a tough one, but one down the road he can look back on and be incredibly proud of everything he has achieved".
With the 31-year-old Scot heading on to court on Monday morning to face Roberto Bautista Agut in the first round there was no need for Federer, still going strong at 37, to play games. "I've always been focused on tactics and winning and finding a way". I know that will be hard.
The avid Liverpool fan also visited the less sunny climes of Anfield to see her beloved team in action, indulging in the local fare after cheering Jurgen Klopp's men on to victory.
"I'm playing good tennis".
For me, I've got Novak facing off against Kei in the quarterfinal, and - given his track record against the Japanese player (15-2 over the years) - I've got Novak advancing through to the semis. "I have a lot of places that are very special to me, thankfully".
'The way I play tennis, maybe it's smoother than the other guys, ' he said. "I can't believe it's already been a year".
"I'm still feel a little behind but that will come with more matches - hopefully more in the main draw". Wozniacki revealed at the seasonending WTA Championships that she'd been diagnosed with rheumatoid arthritis, so she spent much of the off-season resting and recuperating and getting ready for 2019.
She achieved a career milestone previous year to claim her maiden Grand Slam at Melbourne Park, but also revealed she was suffering the debilitating auto-immune condition rheumatoid arthritis. Among those looking to halt Serena's charge: world number one Simona Halep, defending champion Caroline Wozniacki and US Open victor Naomi Osaka.
Wins at Wimbledon and the US Open last summer propelled Djokovic back to the top of the pile, an wonderful achievement having dropped out of the top 20 earlier in the year as he recovered from elbow surgery.
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