|Dates: 23 July-8 August Time in Tokyo: BST +8|
|Coverage: Watch live on BBC TV, BBC iPlayer, BBC Red Button and online; Listen on BBC Radio 5 Live, Sports Extra and Sounds; live text and video clips on BBC Sport website and app.|
Daniil Medvedev struggled to breathe in the Tokyo heat on Wednesday, asking the umpire who would be responsible if he died during his Olympic tennis match.
While he was able to finish his match, that was not the case for Spain's Paula Badosa, who left hers in a wheelchair.
Organisers later announced that from Thursday start times for matches would be pushed back, which players including Medvedev had called for last week.
"I can finish the match but I can die," Russian Medvedev told the umpire.
The 25-year-old world number two took a medical timeout on court and also had the trainer on during a 6-2 3-6 6-2 win over Italy's Fabio Fognini that put him into the quarter-finals.
Chair umpire Carlos Ramos asked Medvedev if he was all right, with the second seed replying: "I'm fine. If I die, will the ITF [governing body the International Tennis Federation] take responsibility?"
Medvedev and world number one Novak Djokovic suggested last week that organisers should push back the start times of tennis matches to avoid the hottest parts of the day when temperatures have reached 33C.
The ITF, which had previously resisted those calls, said that "in the interests of player health and welfare" the matches would start at 3pm rather than 11am from Thursday.
"The decision... is possible due to the outcomes of today's matches across the five competitions being staged and the size of player field, and is designed to further safeguard player health," the governing body said in a statement.
There is an extreme heat policy at the tennis event, which allows players a 10-minute break between the second and third sets if both agree to it.
Medvedev used that time on Wednesday to take a very cold shower.
"Even from the first set I didn't feel good enough with my breathing. That's why I called the physio - I felt like my diaphragm was blocked," he said, adding that he felt it was the most humid day so far in Tokyo.
"And then on the second set, I just had darkness in my eyes, like between every point. I didn't know what to do to feel better. Like I was bending over and I couldn't get my breath together so I was ready to just fall down on the court."
Meanwhile, Badosa said she had suffered heatstroke, which had forced her to retire from her match against Czech Marketa Vondrousova.
"It's a shame to end my participation in this way. It's been a tough ask since day one. We tried to adapt as best we could but today my body hasn't held up as it needed to," she said.
- Day-by-day guide to the Games
- Times and channels for BBC's live coverage
- Listen to the latest Olympics Daily podcast
- Tokyo 2020 medal table