Denver couldn't sign a free-agent signal-caller due to the multi-day incubation period the NFL instituted amid the pandemic, so the team promoted practice squad wide receiver Kendall Hinton to start Sunday.
Lock admitted he and other teammates recently weren't wearing masks for a period of time.
"In a controlled and socially distanced area, we let our masking slip for a limited amount of time," Lock said. "(It's) an honest mistake, but one I will own.
"I sincerely apologize and I fully understand why these safety precautions are so important. Doing the right thing for a majority of the time is not good enough."
The Broncos reportedly expect to be fined and stripped of a draft pick for failing to obey COVID-19 safety protocols.