Daniil Medvedev has withdrawn from the Monte Carlo Masters after testing positive for Covid-19 on Monday.
World number two Medvedev, who was due to kick-off his clay-court season in Monte Carlo, has been moved to isolation.
"It's a big disappointment not to play in Monte Carlo," he said.
Laver Cup
Laver Cup: Best moments so far - featuring Federer, Nadal and Kyrgios
3 HOURS AGO
"My focus is now on, and I look forward to, getting back on the tour as soon and as safely as possible."
Medvedev reached the final of this year's Australian Open and won last year's ATP Finals. He is seeking to progress past the first round of the French Open for the first time this season, having struggled on clay courts in the past.
"Honestly, there's nothing I like on clay," Medvedev told reporters with a smile earlier in the tournament.
There's always bad bounces, you're dirty after playing. I really don't enjoy playing on clay.
The Russian practised with Rafael Nadal yesterday, but the Spaniard and his team were tested on Monday and all results were negative. The next scheduled testing is in three days.
He was scheduled to play the winner of the match between Serbian Filip Krajinovic and Nikoloz Basilashvili of Georgia, after receiving a first round bye.

Djokovic, Federer and Nadal are 'cyborgs of tennis' - Medvedev

Tennis
'Medvedev's game is one-dimensional' - Tsitsipas 'surprised' at what US Open champion achieved
YESTERDAY AT 09:40
Laver Cup
'Looking very sharp!' - Federer helps Nadal with his suit at Laver Cup in 2019
21/09/2021 AT 14:33