ESPN Tennis

MELBOURNE, Australia -- World No. 4 Novak Djokovic will warm up for the Australian Open at the invitational Kooyong Classic, organizers said Wednesday, but champion Roger Federer remains in doubt because of family concerns.

The Swiss No. 1 thrashed compatriot Stanislas Wawrinka to win the title earlier this year before reaching the final of the Australian Open, where he was beaten by Rafael Nadal.

"My latest conversation was about a week ago, and I'm given to understand that the likelihood of [Federer] coming is better than 50-50," tournament director Colin Stubs said. "Obviously it would be the icing on the cake."

Apart from missing the 2008 tournament with glandular fever, Federer has been a fixture at the leafy Kooyong Lawn Tennis Club since 2004 and has used it as a springboard to three Australian Open titles.

The 15-time Grand Slam champion and new father of twin girls has indicated he may scale back his schedule after the U.S. Open.

Djokovic, who beat Federer in the semifinals of the 2008 Australian Open on the way to his first Grand Slam championship, was a welcome surprise for organizers of the Jan. 13-19 event.

"We didn't really expect [him] because in the last couple of years he has decided not to do anything before the Open," Stubs said.

World No. 7 Jo-Wilfried Tsonga, beaten by Djokovic in the Australian Open final in 2008, and 10th-ranked Spaniard Fernando Verdasco have also been confirmed.

Eleventh-ranked Chilean Fernando Gonzalez returns along with giant-killer Marcos Baghdatis of Cyprus, who Federer defeated in the final for his second Australian Open title in 2006.

French Open finalist Robin Soderling and German veteran Tommy Haas will also appear at the tournament, which guarantees all players in the eight-man field three matches on the same surface used at Melbourne Park.

Organizers said they were prepared to wait until the "day before" the tournament for confirmation from Federer before fixing the vacant eighth spot in the field.