Former world number one Novak Djokovic has postponed his long-awaited comeback because of an elbow injury.
The 12-time Grand Slam winner has not played since July's Wimbledon quarter-final and was expected to face Roberto Bautista Agut at the Mubadala World Tennis Championship on Friday.
He said: "This might affect the start of the season and the tournament plan."
British number one Andy Murray, who has also been hampered by injury in recent months, will replace the Serb.
The 30-year-old Scot, who has also not played a competitive match since Wimbledon because of a hip problem, is aiming to make his competitive comeback in Brisbane next week as part of his build-up to January's Australian Open.
Novak Djokovic suffered his elbow injury during this year's Wimbledon quarter-final
Murray had traveled to Abu Dhabi for more practice, but will now play Spanish world number 20 Agut in the one-set match at the exhibition tournament.
Djokovic's withdrawal from this week's event follows that of world number one Rafael Nadal, who is suffering from an ongoing knee injury.
The Spaniard has also pulled out of the Brisbane International but says he still intends to play at the Australian Open.
Djokovic's participation at the first Grand Slam of the year is now in doubt.
Although Djokovic did not reveal how long he would be sidelined for, he raised questions about whether he would be fit to take part in the Australian Open when it starts on Jan. 15.
The 30-year-old added: "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."
"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," he said.
"This might affect the start of the season and the tournament plan, but the decision will be made in the following days."