LONDON >> World No. 1 Rory McIlroy has ruptured a ligament in his left ankle while playing soccer less than two weeks before the start of his British Open title defense.

The Northern Irish golfer gave no indication how long he would be out in the announcement Monday on his Instagram account, only saying that he is "working hard to get back as soon as I can."

"Total rupture of left ATFL (ankle ligament) and associated joint capsule damage in a soccer kickabout with friends on Saturday," McIlroy wrote. "Continuing to assess extent of injury and treatment plan day by day. Rehab already started….. Working hard to get back as soon as I can."

The British Open starts on July 16 at St. Andrews in Scotland.