Gael Monfils, expected to lead France in the Davis Cup final against Serbia in December, is starting to feel the toll of his recent run of good form.
Monfils, who has suffered repeated injuries this year, is 16-4 since the start of the U.S. Open, with a title in Monpellier and losses only to Rafael Nadal, Novak Djokovic, Robin Soderling and Richard Gasquet.
He is defending a final at the Masters in his hometown of Paris this week.
"I'm tired and my knee is a bit sore," said Monfils after his opening win, but added he would be going all out this week.
"The Davis Cup final, there's time. You journalists already want to be there but this is a Masters 1000 tournament that's important and if I have to dive 99 times to win, I'll do it."
The Frenchman next faces Fernando Verdasco, a day after compatriots Richard Gasquet and Gilles Simon went down to Roger Federer and Robin Soderling, respectively. Michael Llodra, the fourth candidate to play singles for France in Davis Cup, takes on Novak Djokovic in the third round.