Mark Davis says the Las Vegas Raiders are looking into why several players were not wearing masks while attending a charity event held by Darren Waller that broke Nevada rules for the coronavirus pandemic and might have violated NFL regulations.

The Darren Waller Foundation held a fundraising event Monday at the DragonRidge Country Club in the Las Vegas suburb of Henderson. Players were seen on video without masks at the indoor event while talking and mingling with guests, who also weren't wearing masks.

"Guys have to be more stringent in fighting the virus," Mark Davis said. "It's still our toughest opponent."

The city of Henderson fined the DragonRidge Country Club $2,000 on Tuesday for four violations of the Nevada governor's COVID-19 emergency directives, including people not wearing masks and having more than 50 people at the event.