Novak Djokovic has pulled out of the Mubadala World Tennis Championship, with Andy Murray being brought in as a late replacement.
Both players have spent the last six months on the sidelines through injury, but the plan had been for Djokovic to feature in Abu Dhabi and Murray to make a competitive return in Brisbane next week.
However, an elbow injury to Djokovic has led to Murray being drafted in to play Roberto Bautista Agut at the exhibition event in the United Arab Emirates.
Both players are hoping to play at next month's Australian Open, but Djokovic has suggested that his schedule may change in the coming days.
The 30-year-old is quoted by BBC Sport as saying: "This might affect the start of the season and the tournament plan, but the decision will be made in the following days."
Djokovic and Murray are now placed at 12th and 16th respectively in the ATP World Rankings.
