Kei Nishikori has withdrawn from the Kooyong Classic exhibition tournament with a left knee injury and the 2012 Australian Open quarterfinalist is in doubt for this year's opening Grand Slam beginning Monday.
The 18th-ranked Nishikori retired from his semifinal match with eventual champion Andy Murray at last week's Brisbane International with the same injury.
After training at Melbourne Park, he felt he was not fit enough to compete at Kooyong and will use the remainder of the week undergoing intensive treatment to try to play in the Australian Open.
The Japanese player said Wednesday ''it's not bad ... let's cross the fingers and hopefully it will be OK.''
On Tuesday, No.12-ranked Juan Monaco of Argentina pulled out of the Kooyong event with a hand injury.