Akron - World No 1 Rory McIlroy's ankle injury which prevented him from playing at the Open Championship forced him to withdraw on Wednesday from next week's World Golf Championships event.
McIlroy, who won the WGC event at Firestone Country Club last year, is also an uncertain starter for the final major of the season the PGA Championship in two weeks at Whistling Straits, where he is also the defending champion.
"Unfortunately, I will not be defending my World Golf Championships Bridgestone Invitational title," McIlroy said.
"Best of luck to all the competitors and I look forward to returning to Firestone in 2016."
McIlroy suffered the injury in early July, rupturing ankle ligaments while playing football with friends.
Second-ranked Jordan Spieth, who won this year's Masters and US Open and was only one stroke off the pace at the Open Championship two weeks ago, could overtake McIlroy for the world No 1 ranking with a victory at next week's WGC event, the same tournament McIlroy won last year to take the top spot.