Lleyton Hewitt's preparations for the Australian Open kick into another gear with a quarter final clash at the Sydney International.

Top seed Hewitt will meet world No.60 Andreas Seppi of Italy in the third match on centre court at Olympic Park.

Hewitt, a four-times winners in Sydney, is still trying to shake a stomach bug but showed huge signs of improvement with Wednesday's 6-1 6-4 win over Austrian Jurgen Melzer.

"I wouldn't say it is all gone just yet. It was a big step in the right direction though," he said.

"I'm pretty pleased with the way I was able to go out there and focus on the job at hand and not worry about how I was feeling at all."

First up (from 1100 AEDT) is an all Russian clash between Igor Andreev and Dmitry Tursunov.

In other men's quarter finals eighth seed James Blake meets Frenchman Arnaud Clement and second seed Nikolay Davydenko will play the winner of the rain-delayed second round match between Paradorn Srichaphan and Ivo Karlovic on Thursday.

An epic battle looms in the women's semi finals between fifth and sixth seeds Justine Henin-Hardenne and Svetlana Kuznetsova.

Henin-Hardenne enjoyed a walkover on Wednesday, Nadia Petrova pulled out with a groin injury, while Kuznetsova trumped tricky Serbian Ana Ivanovic in the only women's match to go the distance.

The other semi final features seventh seed Francesca Schiavone of Italy, who had a walkover against top seed Kim Clijsters who injured her hip during warm up, and eighth seeded Czech Nicole Vaidisova after she led 6-3 3-1 against an ill Daniela Hantuchova.

After four withdrawals from competition on Wednesday, Carlos Moya pulled out of his second round clash with Blake, tournament organiser Craig Watson is hoping there are no more casualties Thursday.

The Sydney tournament has a history of player retirements, Lindsay Davenport, Elena Dementieva and Moya all pulled out here last year, but Watson doesn't believe any players are feigning injury after a few matches to head to Melbourne for the Australian Open early.

"I absolutely do not believe that is the case," he said.

"If (anyone) thinks one match practice is enough then I must be a pretty poor judge.

"Kim (Clijsters) was genuinely depressed and disappointed not to get anymore matches.

"I personally believe there are too many (WTA and ATP) events."

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