Nishikori retires hurt ahead of Wimbledon

Kei Nishikori has been forced to retire from his Halle round-of-16 match with a back injury, putting the world No.9's Wimbledon preparations in some doubt.

World No.9 Kei Nishikori's Wimbledon preparations have suffered a setback after being forced to retire injured from his Halle round-of-16 match against Russian Karen Khatchanov.

The third seed on Thursday needed to take a medical timeout to treat a back injury, before playing on for a few points in the grasscourt tournament. He retired at 2-3 in the first set against the Russian.

The extent of Nishikori's issue is unknown, with Wimbledon starting on Monday week.

Khachanov will play fellow Russians Mikhail Youzhny or Andrey Rublev in the quarter-finals.