TOKYO, July 25 (Reuters) - Britain"s defending Olympic champion Andy Murray pulled out of the Tokyo 2020 men"s singles tournament on Sunday ahead of his first-round match. The 34-year-old, who had been due to play Canada"s Felix Auger-Aliassime, was sidelined by a thigh strain. Murray has been replaced in the draw by Australian Max Purcell. The Scot will continue to compete in the men"s doubles tournament with Joe Salisbury, Team GB said, the pair having won their opening match on Saturday. "I am really disappointed at having to withdraw but the medical staff have advised me against playing in both events," a statement from Murray read. "I have made the difficult decision to withdraw from the singles and focus on playing doubles with Joe." Murray won Olympic gold on Wimbledon"s Centre Court at the London 2012 Games, and defended his title in Rio. He underwent hip surgery in 2018 and 2019, and missed the Australian Open at the start of this year after contracting COVID-19.