World number five Kei Nishikori has been forced to withdraw from the Japan Open after picking up an injury.
The 26-year-old has enjoyed a strong campaign and was hoping to add a third Japan Open title to his CV.
However, the home favourite was forced to retire from his second-round clash with Portugal’s Joao Sousa on Wednesday.
The Olympic bronze medallist suffered a buttock muscle injury when he was leading 4-3 in the first set and will now need to be assessed.
Nishikori was set to take part in the Shanghai Masters on October 9 but will need to wait for his test results to learn the full extent of the issue.
"It was hugely disappointing to have to retire from my match," Nishikori said.
"It is possible that the injury was due to an accumulation of fatigue and stress, but I came into this tournament with a lot of rest and feeling very ready. I will get examined and hope to recover in time for my next tournament."
tagged in Shanghai Masters