Japanese star Kei Nishikori pulled out of the inaugural ATP Cup Monday as he continues to struggle with an elbow injury that has kept him out since the US Open.
The former world number four, who has slipped to 13, said he was disappointed not to be representing his country in Perth at the team event starting on January 3.
"Today, together with my team, we have made this decision as I am still not 100 percent ready to compete at the highest level," he said in a statement.
Nishikori's elbow needed surgery in October and it is unclear whether he will be fit for the Australian Open when the first Grand Slam of the year begins at Melbourne Park on January 20.
Yoshihito Nishioka will replace him as the top-ranked player in Japan's ATP Cup team.