(CNN) -- Tiger Woods has slipped outside of the world's top ten golfers in the new official rankings released Monday.
Woods, whose last win came 18 months ago, is down to 12 in the list, which is still headed by England's Lee Westwood..
It is the first time the American has been out of the top ten since April 1997, just before he won the first of his 14 majors, claiming the U.S. Masters at Augusta.
Woods went on to dominate the rankings, holding the No.1 spot for 625 consecutive weeks from June 2005 until being supplanted by Westwood late last year.
He is set to slip further down the rankings as he is currently sidelined with the left knee and Achilles problems which forced him to pull out of the Players Championship at Sawgrass earlier this month.
It is a worrying development for Woods, who had reconstructive knee surgery in 2008 after winning the U.S. Open title at Torrey Pines, the last of his major titles.
He returned in fine style in 2009 and recorded his last victory at the Australian Masters in November of that year.
But then came the revelations about his private life which led to his self-imposed exile from golf for the early months of the 2010 season.
Woods has remodeled his swing with new coach Sean Foley, but results have been mixed with a playoff loss to Graeme McDowell at the Chevron World Challenge last December the closest he has come to a victory.
Despite his injury, Woods is determined to return for the U.S. Open at Bethseda from June 16-19.
"I'll do whatever is necessary to play in the U.S. Open, and I''m hopeful I'll be there to compete," he told his official website.
Westwood held on to top spot by the skin of his teeth with Luke Donald set to take over from him had he won his Volvo World Match Play final against Ian Poulter.
Donald slipped to a 2&1 defeat to Poulter, who rises to 14th in the new list.