Former world number one Roger Federer has pulled out of the 2021 Australian Open in February.
Djokovic went on to win the title - a record-extending eighth triumph.
“Roger has made strong progress in the last couple of months with his knee and his fitness,” his agent Tony Godsick was quoted as saying by the Associated Press.
"However, after consultation with his team, he decided that the best decision for him in the long run is to return to competitive tennis after the Australian Open.”
Federer had played in the Australian Open main draw every year since his debut in 2000.
“In the end, Roger ran out of time to get himself ready for the rigours of a Grand Slam,” said Australian Open tournament director Craig Tiley. “He’s very disappointed he won’t be coming to Melbourne in 2021.
“The Australian Open has always held a special place in his heart – remember it was Roger who first called the Australian Open the ‘Happy Slam’.
Federer’s withdrawal came just a few hours before the Frenchman Lucas Pouille announced he would also miss the tournament.
Pouille struggled with an injury to his right elbow at the start of 2020. He underwent surgery for the problem in July.
“In agreement with his team, Lucas has decided to come back progressively in order to ensure a competitive return after long months away from the circuit,” said a statement from Pouille's team on Monday.
The 26-.year-old, who has dropped to number 70 in the world after reaching the top 10 in March 2018, will play in second tier challenger events in Quimper and Orleans in France from 25 January.
The start of the 2021 Australian Open in Melbourne has been delayed for three weeks until 8 February due to the country's strict border rules to stem the spread of the coronavirus pandemic.