Defending Olympic champion Andy Murray has withdrawn from the Tokyo Olympics singles competition due to a right quad strain, but remains in doubles, Tokyo 2020 organizers announced. 

Murray, who represents Great Britain, was scheduled to play Canada's Felix Auger-Aliassime on Sunday, but he was replaced by Australia's Max Purcell. 

On Day 1 of competition, Murray and doubles partner Joe Salisbury, who were unseeded, upset the No. 2-seeded French Team of Pierre-Hugues Herbert and Nicolas Mahut in a straight sets victory. 

"I am really disappointed at having to withdraw but the medical staff have advised me against playing in both events, so I have made the difficult decision to withdraw from the singles and focus on playing doubles with Joe," Murray said in a statement. 

Should the British duo go on to win a medal in the men's doubles tournament, Murray would join an exclusive club of tennis players who have won a medal in each Olympic tennis discipline -- singles, doubles, and mixed doubles. Murray took silver in mixed doubles alongside Laura Robson in 2012. Team USA's Venus Williams accomplished the feat at the Rio Olympics, where she won silver in mixed doubles alongside Rajeev Ram.   

Murray, the only tennis Olympian to win back-to-back singles titles, has suffered from hip issues the past few years, requiring several surgeries. He's currently ranked No. 119 in the world and did not qualify outright for Tokyo, instead receiving an invitation reserved for former Olympic or Grand Slam tournament winners.