Rotterdam, the Netherlands: Lleyton Hewitt pulled out of the ABN Amro tournament on Tuesday with a hamstring injury. The seventh-seeded Australian, who won the Rotterdam tournament in 2004, was due to play his opening singles match on Wednesday. Hewitt, a former Wimbledon and US Open champion, injured his right hamstring last week at the ATP tournament in Marseille, France. He retired during his second-round match against Gilles Simon, the Frenchman who went on to win the title. "It is obviously extremely disappointing for me," Hewitt said. "I was coming here for my first trip since 2004, when I won the tournament." Hewitt said he had been having treatment on the injury three times a day. "It's improving, but it's improving slowly," Hewitt said. Earlier this month, Hewitt played two five-set matches in Australia's loss to Belgium in the first round of the Davis Cup. Hewitt was replaced in the first-round draw by the Netherlands' Dennis van Scheppingen, who plays Gael Monfils of France on Wednesday.