Stefanos Tsitsipas found himself the butt of the jokes at the US Open after Andy Murray aimed another jibe at the Greek third seed in the row over long bathroom breaks.

Murray was not in the mood to let the issue slide, though, even after a night sleeping on it.

On Tuesday, he joked it took less time for American billionaire Jeff Bezos to fly into space than Tsitsipas spent in the toilet.

Germany's Alexander Zverev joined in when discussing the favourites for the title, saying: "Stefanos can play well - if he doesn't go to the moon and back for a toilet break, that will also help. I had to, I'm sorry."

While Murray made plenty of people laugh with his dig - with more than 74,000 likes and 14,000 retweets, his third most popular tweet of the year - it was designed to further highlight an issue which he said is "not good for the sport".

"I love that Andy went to sleep last night with emotions running high and has woken up this morning and doubled down on his opinion," former British number one Laura Robson said on BBC Radio 5 Live.

"He's not the first player to complain about this issue."

Why is Tsitsipas gaining a reputation?

Tsitsipas, 23, has gained a reputation as someone who takes long breaks during matches, with Murray becoming the latest to question why.

Murray said he had expected the French Open runner-up to go off court and told his team to prepare for long breaks "if things were not going his way".

Fourth seed Zverev claimed the Greek was doing it "every match".

"It's not normal. It happened to me in the French Open, to Novak Djokovic at the final of the French Open," Zverev said.

"I think in Hamburg against Filip Krajinovic he was complaining, against me in Cincinnati it was ridiculous, and now here again. I think players are catching up on that."

After their recent Cincinnati Masters semi-final, Zverev accused Tsitsipas of using breaks to communicate to his father and coach Apostolos mid-match - which is not allowed on the ATP Tour and which the Greek has strongly denied.

Asked again about that incident at Flushing Meadows on Tuesday, Zverev said: "He's gone for 10-plus minutes. His dad is texting on the phone. He comes out, and all of a sudden his tactic completely changed.

"It's not just me but everybody saw it. The whole game plan changes.

"I'm like either it's a very magical place he goes to or there is communication there."

Tsitsipas said he had "never in my career done that" when asked about the accusation of communication.

"I don't know what kind of imagination it takes to go to that point," he said. "That's not something I want to take seriously because it's absolutely ridiculous to be thinking about that."

Australian player Nick Kyrgios, never one to shy away from controversy, also weighed in.

"How many number twos does this guy take?" he cheekily replied to a US Open Instagram post announcing Tsitsipas' win against Murray.

During his match against Spain's Roberto Bautista Agut, Kyrgios also brought up the issue.

After the Australian complained about having to walk to get a towel, umpire Carlos Bernardes told him it was "part of the game".

"It's not part of the game," Kyrgios replied. "So texting someone is part of the game too? Taking 20-minute bathroom breaks is part of the game?"

Is Tsitsipas doing anything wrong?

Tsitsipas, who has won more matches on the ATP Tour this year than any other player, did not break any rules against Murray.

Players are allowed two breaks for using the toilet and changing clothes in a five-set match, with breaks only permitted at the end of a set.

"A player may request permission to leave the court for a reasonable time for a toilet break," Grand Slam rules state.

As well as the eight-minute break at the end of the fourth set, Tsitsipas also left court for a toilet break at the end of the second set and had a medical time-out for treatment on a foot injury before the fourth set.

Tsitsipas said afterwards he has correctly followed the guidelines throughout his career.

While many of his peers were critical of his actions, Tsitsipas did find himself an ally in American player Reilly Opelka.

Opelka said the flak given to the Greek was "ridiculous" and criticised the reaction of journalists who "have never stepped foot on a tennis court in their life".

"I understand it's getting press because tennis is lame and tennis media sucks and they're terrible," he said.

"To change or to go after, you know, two sets we're drinking, we're hydrating a lot, we have to use the bathroom.

"To change my socks, shoes, my inserts in my shoes, shorts, shirt, everything, the whole nine yards, hat, it takes five, six minutes. Then by the time I walk to and from the court.

"I strictly go to change because it's hot and it's humid.

"If people don't understand that, then clearly they've never spent a day in the life of a professional athlete or come close to it."

Do the rules need changing?

In his post-match interview, Murray called for the rules around bathroom breaks to be changed - a suggestion which has been supported by many in the sport.

British doubles player Naomi Broady agrees and says what Tsitsipas is doing amounts to "gamesmanship".

"He's definitely within the rules but it's the rules that need amending," she said on BBC Radio 5 live.

"There is no time limit for how long you can leave the court for. It's not only the mental side - you're distracting your opponent, trying to break their rhythm - but it's your body.

"Your body has cooled down. Andy had to come out and be the one to serve and I think he got broken."