Tennis-Japan's Nishikori ends 2021 season due to back injury

FILE PHOTO: Oct 9, 2021; Indian Wells, CA, USA; Kei Nishikori (JPN) looks on during his second round match against Daniel Evans (GER) during the BNP Paribas Open at the Indian Wells Tennis Garden. Mandatory Credit: Jayne Kamin-Oncea-USA TODAY Sports

(Reuters) - Japan's Kei Nishikori has ended his season due to a back injury, the former world number four has said.

The 31-year-old, currently ranked 49th in the world, played at last month's ATP Masters 1000 event in Indian Wells, where he lost in the second round to Dan Evans.