Gael Monfils pulled out of the Japan Open Monday with a recurrence of the right knee trouble that has plagued his season, handing a first-round walkover to US Open champion Andy Murray. The 26-year-old Frenchman lost to his compatriot Gilles Simon last week in the quarter-finals in Bangkok, which was only his second event back after being sidelined since May. He also reached the semi-finals last month in Metz. In Bangkok, he admitted how he had grappled with the knee injury, especially as it was unclear when he would be back in action. \"It was four tough months for me, I didn\'t know when I would be back on the court. That is tough on the mind,\" he said in the Thai capital. Monfils reached the Tokyo final in 2010, when he lost to Rafael Nadal. Although the extent of the latest injury is not known, his withdrawal is a blow to the world number 44\'s plans to make a quick return to the top 10. It also removes a difficult hurdle for defending champion Murray, who is returning to competition for the first time since ending Britain\'s 76-year wait for a Grand Slam singles winner in New York last month. \"I played him five times and lost to him a couple of times. He is a great athlete, so that\'s a tough match to start,\" Murray said before the tournament.