Rory McIlroy has increased doubts over being able to defend his crown at the US PGA Championship after being forced to withdraw from the WGC-Bridgestone Invitational which starts on August 6.
McIlroy has been nursing a ruptured ankle ligament that he picked up playing football with friends in early July, and the injury is likely to prevent the world number one from competing at two of the years four major events.
Not only is McIlroy's title defence in doubt, his place as the worlds best golfer could also be in jeopardy. If American Jordan Spieth, who emphatically won the first two major events of the year wins the WGC event, he will replace the Northern Irishman at the top of the rankings.
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Last years Bridgestone Invitational was won by McIlroy, yet medical experts suggest that the 26-year-old could be faced with a three month absence from the sport.
Scottish golfer Richie Ramsey, tweeted that he once suffered a similar injury to McIlroy's, which resulted in a lengthy recovery period.
"I had a full tear of ligaments in my ankle not long ago. It takes a lot longer than you think to heal.
"3 months til I played after tearing ligaments and even then getting my foot to work the right way was tough."
Before sustaining his injury McIlroy was the bookies favourite to succeed at the Open Championship, which was eventually won by American Zach Johnson, after pulling through a captivating three way play-off over Louis Oosthuizen and Marc Leishman at St Andrews.
"Unfortunately, I will not be defending my World Golf Championships-Bridgestone Invitational title," McIlroy said in a statement from tournament organisers on Wednesday.
"Best of luck to all the competitors and I look forward to returning in 2016."
The US PGA, golf's fourth and final major of the year, will be played at Whistling Straits, Wisconsin from August 13.