France's Gael Monfils, ranked 49th in the world, withdrew from next week's ATP event in Montreal on Thursday after suffering an ankle injury in practice.
Also withdrawing from the Canadian hardcourt tuneup event for the US Open was American Mardy Fish, who cited personal reasons. Fish reached the third round at Washington this week before losing to South African Kevin Anderson.
Monfils was to have been a wildcard entry at Montreal. He had previously withdrawn from this week's ATP event in Washington.
"I am frustrated and disappointed," Monfils said. "I sprained my ankle in practice this morning and received treatment before returning to the court to find that it was too painful.
"My doctor strongly advised me to be careful and take 10 days of rest. I am sincerely sorry that I will not be able to play in Montreal."
Canadian teen Filip Peliwo of Vancouver was awarded the final wildcard spot in the field with Monfils' exit, with 65th-ranked Denis Istomin of Uzbekistan replacing Fish.