Novak Djokovic has withdrawn from the Mubadala World Tennis Championship because of pain in his right elbow, placing his participation in the Australian Open in serious doubt.
The 12-time grand slam champion has not played since his defeat to Tomas Berdych in the Wimbledon quarter-finals, subsequently undergoing surgery on his troublesome elbow.
He had been due to face Roberto Bautista Agut on his return at the exhibition event in Abu Dhabi as he prepares for the season's opening major, which gets underway on January 15.
But his plans to feature in Melbourne, and at an event he has won six times, may be in jeopardy after the Serbian indicated the issue "might affect the start of the season and the tournament plan".
In a statement on his website, Djokovic said: "I am terribly disappointed that I am forced to withdraw from the Mubadala World Tennis Championship.
"Unfortunately, in the past few days I started to feel pain in the elbow and after several tests, my medical team has advised me not to risk anything, to withdraw from the tournament and to immediately continue with the therapies.
"I am very sad because I was eager to return to playing official matches. I enjoyed the practices and everything I did to get ready for the start of the season, including the tournament in Abu Dhabi, where I always enjoy playing.
"Now I need to accept this situation, and to wait for the results of the therapies, in order to start playing tennis again and getting back to full rhythm.
"This might affect the start of the season and the tournament plan, but the decision will be made in the following days."
Djokovic's withdrawal follows that of Rafael Nadal, who pulled out to lighten his schedule and will now head to Melbourne without playing a warm-up tournament after also opting not to feature at the Brisbane International.
Stan Wawrinka and Milos Raonic also delayed their returns from knee and calf issues respectively by deciding not to participate in Abu Dhabi.
Andy Murray, whose fitness remains in doubt as he recovers from a hip injury, will now face Bautista Agut in a practice match at 19:00 (local time) to fill the void left by Djokovic.