Japanese world number nine Kei Nishikori was forced to retire injured in the second round at Halle on Thursday but insisted he was hopeful of being fit for Wimbledon which starts on July 3.

The 27-year-old Olympic bronze medallist had treatment courtside but in the end was forced to concede defeat.

"It's very disappointing to retire like this again," said Nishikori, who withdrew from the Halle event last year before his second-round match against Florian Mayer and retired 4-1 down in his 2015 semi-final against Andreas Seppi.

"I was feeling good on the court but hopefully I will be OK for Wimbledon. The doctors say that in a week I should be fine."