Tokyo, Japan, 6 October 2016 | AAP

Australia’s Nick Kyrgios is through to the quarterfinals of the Japan Open following the withdrawal of Czech veteran Radek Stepanek with a back injury.

The walkover means world No.15 Kyrgios will face Cypriot Marcos Baghdatis or Frenchman Gilles Muller in the last eight.

World No.106 Stepanek, who turns 38 next month, failed to take to the court against Kyrgios.

He has been acting as a part-time mentor for Kyrgios, who has risen to 15th in the rankings.

Kyrgios has won two titles this season, in Marseille and Atlanta.

Marin Cilic and David Goffin and Juan Monaco have advanced to the quarters, with top seed Kei Nishikori also pulling out with a back injury midway through the first set of his match with Joao Sousa.

Monaco ended the hopes of James Duckworth, Australia’s only other player in the Tokyo draw.