The Denver Broncos have no quarterbacks. The San Francisco 49ers have no home stadium or practice facility. And the Baltimore Ravens might not have enough players available for their next game, which has already been pushed back twice.

The COVID-19 pandemic caused major disruptions around the NFL on Saturday, again calling into question the league's plan to play a full schedule after several weeks that went relatively smoothly.

All four quarterbacks on the Denver roster are ineligible to play the New Orleans Saints on Sunday because of coronavirus concerns.

Starter Drew Lock, backup Brett Rypien and practice squad veteran Blake Bortles were deemed high-risk close contacts with No. 3 quarterback Jeff Driskel on Wednesday, the day before Driskel tested positive for COVID-19.

A person familiar with the league's investigation, speaking on condition of anonymity to discuss the sensitive topic, said the four QBs apparently weren't wearing their masks the whole time they were together as required by the league's pandemic protocols.

In a statement released Saturday night, the Broncos confirmed reports that Lock, Rypien and Bortles were ordered off the practice field Saturday and into isolation after being identified as high-risk COVID-19 close contacts.

The team was scrambling to prepare practice squad rookie receiver Kendall Hinton and No. 3 running back Royce Freeman to share snaps at quarterback Sunday.

"I'm not one to complain, but @NFL y'all can't possibly send us into a game without a QB," Denver tight end Noah Fant wrote on Twitter.

The Ravens, meanwhile, put six more players on the COVID-19 list, which is for players who have either tested positive for the virus or had close contact with an infected person. Baltimore had already disciplined an unidentified staff member for violating protocols, and the outbreak — the worst on any team this season — left the Ravens with three defensive linemen and one quarterback available.

The Ravens' game at rival Pittsburgh was initially scheduled for Thanksgiving and was moved to Sunday before being postponed again for Tuesday. Some Steelers players complained about their schedule being disrupted again because of another team's failure to contain an outbreak. But the Steelers placed starting running back James Conner on the COVID-19 list Saturday, joining three other teammates.

NFL Commissioner Roger Goodell has warned all 32 teams that forcing changes to the schedule could lead to them being stripped of draft choices or even forfeiting games. The league has thus far avoided any forfeits and was on track to complete its regular season on time.

But the league has few options should the Baltimore-Pittsburgh game need to be further delayed. The league also moved Thursday night's matchup between Baltimore and Dallas to Dec. 7.

For the 49ers, the latest complication arose from the local government trying to contain the spread of the virus in the county where they practice and play their home games. Santa Clara County banned all contact sports from holding games and practices for the next three weeks.

The ban was to take effect Monday and set to last until Dec. 21. The 49ers have home games scheduled for Dec. 7 vs. Buffalo and Dec. 13 vs. Washington at Levi's Stadium in Santa Clara. One option could be to play at the Oakland Coliseum — the Raiders' old home — or possibly the Giants' baseball stadium in San Francisco, if those cities don't adopt similar bans.

Elsewhere in the league on Saturday:

•The Colts will be without rookie running back Jonathan Taylor on Sunday. He is one of three Indianapolis starters sitting out because of COVID when the team plays Tennessee for the AFC South lead.

•The Saints placed Terron Armstead on the COVID-19 list, leaving the starting left tackle ineligible to play at Denver.

•The Raiders said running backs coach Kirby Wilson won't coach this week because of COVID-related reasons.