Japan’s Kei Nishikori is aiming to return to the court in six months after having left hip surgery, the men’s singles former world No. 4 said on his app Tuesday. The 32-year-old had said on Jan. 7 his struggle with the injury since the end of last year ruled him out of the Australian Open, with his most recent tournament being the ATP Masters 1000 Indian Wells in October. “After trying several different rehab options I have decided (together with my medical team) to have arthroscopic hip surgery this week,” wrote Nishikori, currently ranked 46th in the world. “I will work as hard as I can and …