Stomach bug hits Indian Wells
Russian Zvonareva, the ninth seed in the WTA tournament, withdrew from her scheduled third-round match on Sunday, gifting Czech Klara Zakopalova a spot in the next round.
Earlier in the day, Frenchman Monfils, the 14th seed in the ATP event, American Vania King and Austrian Juergen Melzer also pulled out because of stomach problems.
"I'm really sorry to withdraw from the tournament but unfortunately I'm not feeling well enough to compete today," Zvonareva, a 12-times winner on the WTA Tour, said in a statement.
"Hopefully I can recover from the illness and play in the next event (in Miami) but today I just don't feel that I can go out there and perform well enough."
King, who won her first WTA title in Paris last month, had already played two matches in the California desert and her pullout handed 18th-seeded German Angelique Kerber a place in the fourth round.
King, who had never reached the fourth round at Indian Wells, tweeted on Sunday: "Just spent one of the worst nights of my life (gruesome details) fever, vomiting, diarrhea..all at the same time..caught a bug from someone."
Melzer, who had been beaten in the second round of the ATP tournament, pulled out of the men's doubles on Sunday.
Kohlschreiber withdrew before his second match of the week, Seppi and Rybarikova retired during their second-round encounters while Mattek-Sands, who lost her first-round match in the singles, is still competing in the women's doubles.
In a statement issued on Sunday, health officials in the Palm Springs area said the virus had spread across the Coachella Valley, resulting in symptoms of nausea, vomiting, fever and diarrhoea.
"It (the virus) is self-limited and lasts between 24 and 48 hours," the Eisenhower Medical Center said. "It is transmitted by air and direct contact and not passed via food.
"... we have seen increases in overall visits to the emergency department by about 15 percent over the past week. We have seen fans and players at the tournament experience these symptoms as well."