Andy Murray has announced his withdrawal from the Australian Open due to a long-term hip injury.
The former world No 1's participation was thrown into jeopardy earlier this week when he pulled out of the season-opening Brisbane International.
Murray's decision to pull out of the Australian Open comes on the same day as Japan's world No 22 Kei Nishikori announced he would miss the first grand slam of the year in Melbourne starting January 15 to continue his rehabilitation from a long-term wrist injury.
Murray, 30, suffered the injury last year and has not played on the ATP tour since losing in the quarter-finals at Wimbledon to Sam Querry.
"Sadly I won't be playing in Melbourne this year, as I am not yet ready to compete," the Scot said in a statement.
"I'll be flying home shortly to assess all the options but I appreciate all the messages of support and I hope to be back playing soon."
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Australian Open's tournament director Craig Tiley said he respected what was a "very hard decision for Andy".
"We are fully aware that Andy has been going through a difficult period with his hip and that he's done everything possible to prepare for the Australian summer," Tiley added.
Murray's withdrawal comes amid a string of injury concerns that have plagued some of the world's top players and cast doubt on their participation in Melbourne in just over 10 days time.
Nishikori, who has not played competitively since last August after suffering a torn tendon in his right wrist during a practice session at Cincinnati, also pulled out of earlier Thursday, saying he is "just not ready 100 per cent to come back yet in best of five set matches."
Former world No 1 and six-time Australian Open champion Novak Djokovic has not played since a right elbow issue forced him to quit Wimbledon in the quarter-finals in July and has already cancelled scheduled appearances at the Mubadala World Tennis Championship in Abu Dhabi and the Qatar Open in Doha this past week.
He said he intended to test the injury next week at two exhibition events in Melbourne next week, the Kooyong Classic and Tie Break Tens.
There are also concerns over the participation world No 1 Rafael Nadal, who missed Abu Dhabi and Brisbane with a knee injury, and 2014 Australian Open champion Stan Wawrinka is also battling to regain full fitness.