After battling to qualify for her 16th US Open quarterfinal on Monday night, Serena Williams threw doubt on whether she will play at Roland Garros later this month, citing worries about the organisers' plans to host a crowd. Last month the 23-time grand slam champion said she definitely saw herself competing at the French major if it went ahead, but following updates to protocols in recent days, Williams was less sure. Due to more flexible conditions at the US Open, Williams is currently staying at a private home in New York, while forking out for 24-hour security to make sure she does not leave her bio-secure bubble. But it was announced on Sunday that the French Open – which starts on September 21 – will take a stricter approach, with all players required to stay in one of two tournament hotels. "I was hoping to stay at my apartment in Paris, but I'm just taking it a day at a time," Williams said after her fourth round win over Greek No 1 Maria Sakkari on Monday night, declining to give a definitive answer as to whether she will play. "[The organizers] are doing the best that they can. So I can't point fingers." When it was pointed out to her that the French Open had still not ruled out hosting fans at 60 per cent capacity though, Williams became more concerned - citing her reduced lung capacity which puts her in a higher risk category when it comes to coronavirus. "If there are fans, then we should be able to stay elsewhere," she said. "I'm super conservative because I do have some serious health issues, so I try to stay away from public places, because I have been in a really bad position in the hospital a few times. "I'm going to have to make the best decision for my health. Maybe it will be good for me to talk to the organizers just to see how that works with the crowd and how we will be protected. But I think it should be okay... I don't know what the number [of spectators] will be and how close they will be. I still have some questions, but I'm really, ironically, focused on New York. It's hard because these Grand Slams are so close to each other this year." Sakkari also voiced doubts, saying "it doesn't make sense to have fans and have us in a bubble", while British doubles player Jamie Murray echoed the worries after his and Neal Skupski's quarter-final loss: “It increases the chances of players picking stuff up if they are in or around members of the public... Having been here and seen how much of a lockdown it was, you feel safe. The thought of going into play with members of the public, how do they manage that?" Coronavirus cases are spiking in Paris, and on Sunday French Tennis Federation president Bernard Giudicelli said that it was “too early to say” whether any fans would be allowed. Seeing Williams's thoughts may prove a factor in their decision-making, especially if she wins her record-equalling 24th grand slam title in New York, which she remains on track to do despite a tough challenge from Sakkari on Monday night. When Williams lost to the Greek No 1 13 days ago at the Western & Southern Open, she described her growing inability to close out matches as “like dating a guy that you know sucks". On Monday, at Arthur Ashe Stadium against the very same opponent, she definitely dumped him - but the 38-year-old had to recover from a break down in the third set to get the win, in what was a mesmerising and physical fourth round tie. "Thank God I got rid of that guy," she joked after the 6-3 6-7(6) 6-3 victory. "Never want to see him again. He was the worst." Her 100th win on the Flushing Meadows main court, she will need to recover from the 2 hour 27 minutes three-setter, her second in a row at the tournament for her quarter-final on Wednesday. She plays Bulgaria's Tsvetana Pironkova - competing in her first tournament since Wimbledon 2017, after taking time out to have her first child.