NEW YORK (CBSNewYork) — The hot and humid weather continues to cause problems at the US Open and some notable players have started to sound off about the poor playing conditions.

Superstars Roger Federer and Novak Djokovic have both taken issue with the decision to leave the roof at Arthur Ashe and Louis Armstrong Stadiums open during matches.

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Federer, a 20-time Grand Slam champion, was ousted on Monday by John Millman, an unseeded player from Australia. After the match, though he didn’t blame the roof being opened for his loss, said the conditions were not good for tennis.

“It was just one of those nights, I guess, I felt I couldn’t get air. There was no circulation,” Federer said.

Djokovic was a bit more blunt following his straight-set win over Millman on Wednesday in the quarterfinals.

“I think that this tournament needs to address this,” Djokovic said. “We, as players, are grateful that we have the roof, because then the rain will not interrupt the matches. But there is no circulation of the air at all, especially court level.”

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That point was illustrated during the second set when, in a bizarre moment, a drenched Millman was allowed to leave the court after the fourth game to change. Under normal conditions, an umpire would permit such a change only after odd-numbered games.

Despite this being the first US Open with the expensive roofs in place, the new coverings only closed briefly on Aug. 31 due to passing rain showers.

On Thursday, officials suspended all junior and wheelchair matches that were scheduled to take place after 12 p.m. due to the high heat. It marked the fourth straight day the extreme heat rule was put into effect.

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That policy also allows for a 10-minute break between the second and third sets of women’s singles semifinal matches on Thursday night.