World number four Kei Nishikori has withdrawn from the Western and Southern Open, citing a hip injury.

The Japanese US Open runner-up was on an eight-match winning streak before losing to Andy Murray in straight sets in the Rogers Cup semi-finals.

Nishikori, 25, appeared to be tiring during the 6-3 6-0 loss to the Briton, who went on to beat Novak Djokovic in Sunday's final.

With the US Open starting on August 31, Nishikori has decided not to play in Cincinnati.

"Sad news as Kei Nishikori has withdrawn from #CincyTennis due to a hip injury," the tournament tweeted.

"Wishing the World No.4 a speedy recovery!"

Nishikori also missed the event last year, with his best result coming in 2012 when he reached the last 16.