World number one Henin, nursing a sore shoulder, has dominated the women's tour with six titles, capped by her Toronto triumph earlier this month. She also won her fourth French Open crown and third in a row at Roland Garros.
The Williams sisters, Serena and Venus, have snagged the other two grand slams in announcing their return to the spotlight after a barren 2006.
But they too have injury issues.
Australian Open champion Serena has struggled with an injured left thumb, while Venus is suffering tendinitis in her right knee.
They are not the only top guns banged up at the end of an arduous season.
Defending U.S. Open champion Maria Sharapova pulled out of this month's Los Angeles semi-finals with a lower left leg strain after the Russian was bothered earlier in the year by a bad shoulder that limited her to one 2007 WTA Tour title.
Champions often find a way to battle through injury as 25-year-old Henin proved in snaring the Rogers Cup in Toronto after receiving treatment before winning the final against world number three Jelena Jankovic of Serbia.
The battling Belgian scored her seventh victory over Jankovic without defeat and said she was looking forward to mounting a campaign to repeat her 2003 U.S. triumph. Last year she lost to Sharapova in the final.
"It's going to be sore for a few days," she told reporters.
"I know it because that's a pain I've known for a couple of years. I'll be fine for the Open."
Serena Williams, 25, ended 2006 ranked 95th but erased any doubts she still belonged among the tennis elite by launching the new tennis season with her third Australian Open title and eighth grand slam singles victory.
Her sister Venus, 27, won her fourth Wimbledon championship this summer and will be gunning for her third U.S. Open victory.
The elder Williams, now ranked 13th, last won it in 2001, while ninth-ranked Serena seeks to reprise her 2002 triumph at the National Tennis Center.
Rounding out the leading contenders for the final grand slam event of the year are 2004 champion Svetlana Kuznetsova of Russia, ranked fourth, and a pair of young players on the move up the rankings.
Fifth-ranked Ana Ivanovic of Serbia won earlier this month in Los Angeles for her second title of the year, while world number six Anna Chakvetadze of Russia won summer hardcourt titles in Cincinnati and Stanford to run her 2007 haul to four victories.
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