Golf:Luke Donald will become the fourth world number one in less than six months if he wins this week's Heritage tournament at Hilton Head Island, South Carolina.

Donald will leapfrog top-ranked Martin Kaymer, who is not playing this week, and number two Lee Westwood even if the latter wins the Indonesian Masters because the Heritage carries more rankings points than the Asian Tour event.

Westwood, deposed as number one by Kaymer earlier this year, can retain top spot with a victory in Indonesia if his fellow Englishman fails to win at Hilton Head.

"The scenario is pretty simple," rankings manager Ian Barker said today. "Luke Donald and Lee Westwood have the chance to pass Martin Kaymer if they win their respective tournaments. If they both win Luke will be number one, if Lee wins and Luke doesn't then Lee will be number one.

"If neither of them win, Martin Kaymer will remain at the top."

World number three Donald, 33, who won the WGC-Accenture Match Play in February and tied for fourth at this month's US Masters, has never been top of the rankings.

Westwood is hoping to mark his 38th birthday on Sunday by snatching the Indonesian title.

"It will be difficult as there are a lot of strong players out here in Asia and you have to play well to win," he told reporters at the Royale Jakarta Golf Club.

Number five Graeme McDowell is also in action at the Heritage but cannot reach the top of the rankings this week. Fourth-ranked Phil Mickelson and number six Tiger Woods, who was knocked off top spot by Westwood in November, are not playing this week.