World top-ranked golfer Rory McIlroy announced on Monday he suffered a ruptured anterior ligament to his left ankle while playing soccer with friends over the holiday weekend.

According to ESPN, it's unknown how long the injury will keep McIlroy sidelined or if he will be able to defend his titles. After making the announcement, McIlroy posted a picture of himself on Instagram with his leg in a boot and balancing himself on crutches.

"Continuing to assess extent of injury and treatment plan day by day," he wrote. "Rehab already started. ... Working hard to get back as soon as I can."

McIlroy's spokesman Sean O'Flaherty later confirmed he will miss the Scottish Open which starts later this week, but remained vague about his prospects of competing at the Open Championship which kicks off on July 16, at St. Andrews.

McIlroy had been a 5-1 favorite at St. Andrews, but those odds dipped to 8-1 after news of the injury began to spread, according to the Westgate, Las Vegas SuperBook. Meanwhile, Jordan Spieth climbed from 6-1 to 9-2 odds for the tournament, now making him the betting favorite.

"Unlucky, obviously," said fellow veteran Luke Donald. "I would never say, 'Don't play football or don't do these thing.' You don't want to live in a bubble. It's just unlucky timing, especially this time of the year."

McIlroy bagged last year's Open title at Royal Liverpool, leading from wire to wire and taking a six-shot lead into the final round. He also won the PGA Championship to join legends Jack Nicklaus, Tiger Woods and Bobby Jones as the only players in the past century to win at least four majors by the age of 25 or younger.