Tommy Haas withdraws from Shanghai Masters

Juan Martin del Potro has progressed to the quarter-finals of the Shanghai Masters.

The sixth seed reached the last eight after being awarded a walkover win against Tommy Haas.

Haas, who had recorded 6-4 6-4 wins over Sam Querrey and Daniel Brands, was unable to take to court against Del Potro due to a back injury.

Del Potro will now face either Nicolas Almagro or Tomas Berdych for a place in the semi-finals.