"Tursunov had to withdraw from the tournament with a painful left knee. He has been suffering from the injury for a week now and will undergo an MRI scan," organisers said.
Fifth seed Gaudio dropped only six games when he began the defence of his title against Frenchman Julien Benneteau on Monday. The Argentine will not be in action again before he faces either Felix Mantilla or Jiri Novak on Friday.
"I tried to warm up and then I heard he wasn't going to play," said Gaudio.
"I would have preferred to have won the match obviously but these things happen."
Results from the Men's Singles Round 2 matches:
10-David Nalbandian (Argentina) beat Tomas Berdych (Czech Republic) 6-3 6-2 6-1
5-Gaston Gaudio (Argentina) beat Dmitry Tursunov (Russia)WO