LONDON, Sept. 26 (Xinhua) -- Four-time world champion Ronnie O' Sullivan has slipped to 17th in the world rankings, the first time since he entered the game's elite 19 years ago.

O'Sullivan, who won his fourth world title in Sheffield last May, missed the Shanghai Masters, the Australian Open and the Wuxi Classic.

Mark Selby becomes world No. 1 and Judd Trump and John Higgins are ranked second and third respectively. China's Ding Junhui is ranked 13th.

The 36-year-old eventually agreed a players' contract in August and is set to feature at the International Championship in China next month.

O'Sullivan has confirmed to take part in the inaugural International Championships to be held in Chengdu, Southwest China next month.