MIAMI (AFP) - World number ones Roger Federer and Justine Henin could have a tricky time at the WTA and ATP Masters Series event that begins here on Wednesday thanks to their draws.

Swiss star Federer jumps back onto the court after an upset semi-final loss to American Mardy Fish last weekend at Indian Wells, California.

Federer, seeking his first title of 2008, has a first-round bye and will then face France's Gael Monfils or US wild card John Isner, whose serve power tested Federer in a 6-7 (4/7), 6-2, 6-4, 6-2 third-round victory on his way to last year's US Open crown.

Federer could meet Australian Lleyton Hewitt in the fourth round of the 3.7 million-dollar hardcourt event, American Andy Roddick or France's Jo-Wilfried Tsonga in the quarter-finals and Russian Nikolay Davydenko in the semi-finals.

Following Federer on the seed list are reigning French Open champion Rafael Nadal of Spain and reigning Australian Open champion Novak Djokovic of Serbia, who beat Fish in Sunday's Indian Wells final.

Nadal faces either Argentina's Sergio Roitman or a qualifier in his round two opener. Djokovic would meet a qualifier or Argentina's Agustin Calleri.

Next among the seeds are Davydenko, Spain's David Ferrer, Roddick at sixth, Argentina's David Nalbandian and France's Richard Gasquet.

On the women's side, Henin returns after nearly one month off since losing a Dubai quarter-final to Italy's Francesca Schianove. Henin has already taken titles this year in Sydney and Belgium and is 12-2 on the season.

Henin has a bye into a second-round matchup with either Angelique Kerber of Germany or Uzbekhistan's Akgul Amanmuradova.

Defending Miami champion Serena Williams and reigning Wimbledon champion Venus Williams, who skipped last week's event at Indian Wells, are back in action and could meet each other in the semi-finals.

Sixth seed Venus opens in round two against either fellow American Jill Craybas or Poland's Maria Domachowska while eight-seeded Serena would meet Czech Klara Zakopalova or Romanian Edina Gallovits in her second-round debut.

Henin and Serena could meet in the quarter-finals in a rematch of last year's Miami final, in which Williams rallied to defeat Henin 0-6, 7-5, 6-3 for her 28th career crown. Serena also won a title this year at Bangalore.

Possibly awaiting in the semi-finals would be Venus Williams or Russian third seed Svetlana Kuznetsova, the runner-up in last weekend's WTA event at Indian Wells.

Serbian world number two Ana Ivanovic, who lost to Maria Sharapova in the Australian Open final, won her sixth career title by defeating Kuznetsova 6-4, 6-3 in the Indian Wells final.

Sharapova dropped out of this event, citing fatigue.

Venus Williams won Miami titles in 1998, 1999 and 2001 but was ousted by Sharapova in the third round here last year.

Ivanovic opens in round two against France's Emilie Loit or Spain's Virginia Ruano Pascual with American Lindsay Davenport a possible third-round foe. She could meet Slovakian seventh seed Daniela Hantuchova in the quarter-finals.

Serbian fourth seed Jelena Jankovic will open against a qualifier or Swede Sofia Arvidsson while Russian fifth seed Anna Chakvetadze, her possible quarter-final foe, opens with either France's Alize Cornet or Austrian Tamira Paszek.