Washington quarterback Dwayne Haskins has been fined $40,000 (£29,400) and removed as a captain after being filmed at a party without wearing a mask.
The fine is thought to be the largest in the NFL for breaking Covid-19 protocols and more than half of 23-year-old Haskins' weekly salary.
"My actions were immature and unacceptable," he said.
"I put my team-mates, coaches and staff members at risk and let the fans and the organisation down. I take full responsibility and accountability for that.
"Being a quarterback in this league comes with a big responsibility and leadership, and I failed to live up to those standards with my actions.
"I fully understand the mistakes that I've made and the circumstances that come with it, and I'm OK with that because I deserved it."
Haskins is still allowed to take part in practice for Washington, who are preparing to play the Carolina Panthers on Sunday.
But to be allowed to participate, he must have two coronavirus tests every day and wear a mask under his helmet that includes a face shield.
Washington head coach Ron Rivera confirmed Haskins will start this weekend's match if fellow quarterback Alex Smith is not fit to play.
Last Sunday saw Haskins make his first start since early October because of Smith's calf injury. Haskins completed 38 of 55 passes - for 295 yards with one touchdown and two interceptions - in the 20-15 home defeat by Seattle.
