Updated

By Ian Ransom

MELBOURNE (Reuters) - Croatia's Ivan Ljubicic has taken the final spot at this week's Kooyong Classic after champion Roger Federer withdrew from an event he traditionally uses as a final warm-up for the Australian Open.

The 30-year-old Ljubicic, a nine-time ATP tour champion, completes a strong eight-man field at the Melbourne invitational, boasting world number three Novak Djokovic of Serbia and Argentina's U.S. Open champion Juan Martin del Potro.

His replacement, Ljubicic faces a baptism of fire in his first match on Wednesday's opening day at Kooyong Lawn Tennis Club, having drawn second-seed Del Potro, who overcame a spate of injuries late last year to finish the season in solid form.

The towering Argentine is playing his first tournament since finishing as runner-up at the season-ending ATP Tour Finals in November, after enjoying a holiday with family and friends which he described as "good preparation" for next week's Open.

"So I will be looking for another grand slam here in Melbourne," the 21-year-old said.

SWINE FLU

The 2008 Australian Open champion and top seed Djokovic will play experienced German Tommy Haas, who joked about being brought down by swine flu late in the season after his surprise semi-final appearance in Wimbledon last year.

"Caught the swine flu -- which I still have ... So, yeah, just looking forward to a new start. Glad I got the toughest opponent here in the first round against Novak."

"I'm sure he's looking forward to avenge himself against me," added the 31-year-old, who upset Djokovic at the quarter-finals at Wimbledon.

Swedish world number eight Soderling faces Jo-Wilfried Tsonga on Wednesday after an all-Latin battle between Chile's Fernando Gonzalez and ninth-ranked Fernando Verdasco of Spain.

Tsonga, who burst into the limelight with his run to the 2008 Australian Open final, was quick to dismiss concerns about his fitness after a wrist injury forced his withdrawal from the last week's Qatar Open.

"My wrist is okay," the 10th-ranked 24-year-old said. "I'm really antsy and I'm pleased to play against the... best player(s) in the world."

Kooyong, seen as a form guide for the Australian Open which begins on Monday, guarantees players three matches on the same surface used at Melbourne Park.

British world number five Andy Murray, craving a final thorough workout before his tilt for a maiden grand slam next week, would also play an exhibition match at the tournament on Thursday with an opponent yet to be named, organizers said.

(Editing by Patrick Johnston)