The International Tennis Federation (ITF) has confirmed matches at the Tokyo Olympics will now start later in the day after concerns over player health and welfare.

World numbers one and two Novak Djokovic and Daniil Medvedev have been among the players to complain about games starting too early in the day, citing the heat and humidity at Ariake Tennis Park as a major issue.

Indeed, on Wednesday, 25-year-old Medvedev struggled with the conditions as he battled to a 6-2 3-6 6-2 win over Fabio Fognini.

Despite being allowed 10 minutes off court at one stage, Medvedev was in visible discomfort during the last-16 tie, and had two medical timeouts before being asked by chair umpire Carlos Ramos whether he could continue.

"I can finish the match but I can die," the Russian replied to Ramos, per ESPN. "If I die, are you going to be responsible?"

The 72 per cent humidity meant 31 degrees Celsius felt like 37 degrees Celsius on the heat index. Medvedev was not the only player to suffer on Wednesday, with Paula Badosa having to be taken from the court in a wheelchair as she retired against Marketa Vondrousova due to heatstroke.

Earlier in the week, Medvedev had questioned the approach of starting matches in the late morning, while top seed Djokovic suggested scheduling the first games for 15:00 local time.

The ITF has now agreed, with start times pushed back to 15:00, meaning the majority of matches in the closing stages of the Olympic tennis will be played during the slightly cooler evening hours.

"In the interests of player health and welfare and following extensive consultation, the ITF has announced a change of schedule due to the increasing heat and humidity currently being experienced in Tokyo," an ITF statement read.

"The decision to start matches at 3pm JST from Thursday is possible due to the outcomes of today’s matches across the five competitons being staged and the size of the player field.

"[The decision] is designed to further safeguard player health."