Perth: Japanese star Kei Nishikori pulled out of the Australian Open and 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 No. 4, who has slipped to 13, said he was disappointed not to be able to begin his season as hoped for in January. "Unfortunately I have to pull out of the ATP Cup and the Aussie Open," he said in statement.