Doubt was cast over whether Djokovic would be fit to play in the Australian Open, which starts on Monday, when he withdrew from warm-up events in Abu Dhabi and Doha.
"All these things all play into it but at the end of the day I've been in this position thankfully many times before".
With Rafael Nadal and Novak Djokovic among the walking wounded and Serena Williams already deciding not to defend her title, injuries and absentees have been the focus of attention ahead of the Australian Open.
The Australian Open will begin on January 15.
First up, the 36-year-old Swiss will play Ajaz Bedene of Slovenia. A handy consultant last season, four-time champion Andre Agassi is said to be now planning a late dash Down Under to re-join the team after a snowboarding mishap back home.
At the US Open and World Tour Finals, last year's Australian Open champion Federer appeared worn out, losing to Del Potro and Goffin in the latter stages.
No. 2 Caroline Wozniacki, who hasn't won a major and last appeared in a Grand Slam final in 2014, is on the bottom half of the draw with Williams and has French Open champion Jelena Ostapenko and last year's Australian semifinalist CoCo Vandeweghe in her quarter.
Six-time champion Djokovic has a shot at surpassing Roy Emerson to become the only male player with seven Australian Open titles in tennis history.
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Djokovic is poised to return to action after recovering from his injury-plagued 2017 and he's expected to challenge for the title as well, but the Serb star says it is Federer and Nadal who should be feared most. The two could face each other in a blockbuster semi-final, should Djokovic get past fourth seed Alexander Zverev in the fourth round.
He returns to the Australian Open, where he lost a thrilling five-set final to long-time rival Roger Federer in 2017, after overcoming his chronic knee problems just in time and hoping to continue last year's progress under new coach Carlos Moya.
Top-ranked Simona Halep is in the same half as Wimbledon champion Garbine Muguruza, who has a hard quarter containing former Australian Open champions Maria Sharapova and Angelique Kerber.
"He could always get picked off early", McEnroe said.
If you look at their previous head-to-head records it is clear just how much of a tricky opponent Djokovic has proved for the pair, with him winning just over half of the matches against both Nadal and Federer. Anything can happen. It's a Grand Slam.
There has been little to cheer since the turn of the century and the last time an Australian made it to the men's final at Melbourne Park was Lleyton Hewitt in 2005.
Now ranked No47, she could face the 14th seed Anastasija Sevastova in the second round, Angelique Kerber - the 2016 champion - in the third round and, potentially, Garbine Muguruza, the Wimbledon champion, in the fourth round.
Cilic, the 2014 U.S. Open victor and last year's beaten Wimbledon finalist, will be expected to face Nadal in the last eight, with Pablo Carreno Busta (10) and Pablo Cuevas (31) also lurking, as well as Gilles Muller (23) - Nadal's conqueror at Wimbledon last year.