Second-ranked Daniil Medvedev has withdrawn from the Monte Carlo Masters after testing positive for coronavirus on Tuesday, April 13.
The 25-year-old Russian has been placed in isolation and will be monitored by the tournament physician.
Medvedev had a first-round bye for the clay-court tournament, which began on Monday.
The ATP said Medvedev has been placed in isolation. His condition is being assessed by the tournament doctor and the ATP medical team.
Medvedev practiced with world number three and 11-time Monte Carlo champion Rafael Nadal on Monday.
The Monte Carlo Masters takes place from 12-18 April.