The Baltimore Ravens temporarily closed their training facility Monday morning after two players, running backs Mark Ingram II and J.K. Dobbins, and other members of the organization tested positive for the coronavirus.

The Ravens reopened their facility later Monday and planned to conduct a light walk-through practice, Coach John Harbaugh said. Their game Thursday night in Pittsburgh against the unbeaten Steelers remained on as scheduled, according to Harbaugh and another person familiar with the NFL’s planning.

The Ravens’ issues came as the NFL further toughened its coronavirus protocols. The league told teams in a memo Monday that, beginning with this week’s Thanksgiving games, all players who are on the sideline during a game (those not substituting or preparing to take the field and not wearing their helmets) must wear masks or double-layered gaiters.

“Players who fail to wear masks on the sidelines will be subject to discipline,” the NFL’s memo said. “Clubs are required to enforce these rules. Violations by players and/or staff will result in accountability measures being imposed upon the Club. It is strongly recommended that each Club designate one or two individuals in the Bench Area to ensure compliance with these rules.”

Coaches and team staffers already were required to wear masks while on the sideline during games. Sideline mask-wearing previously had been recommended for players during games but not required; it was required of players before and after games. Monday’s memo by the NFL also outlined a reduction to the number of players allowed to travel to a road game and further restrictions on access to team facilities while players and coaches are present.

Harbaugh confirmed during a video news conference that Ingram and Dobbins had tested positive. According to Harbaugh, defensive tackle Brandon Williams was placed in a five-day quarantine after being identified as a high-risk close contact. The three players were placed on the Ravens’ covid-19 reserve list and will miss the game in Pittsburgh.

“There’s nobody else besides that,” Harbaugh said. “There’s nobody else that has it. I think our players did a great job on the sideline with masks, a great job in the locker room. We tried to follow the protocols throughout the game and throughout the weekend at the hotel and the meetings during the week. Our guys have done a good job of that. So I’m appreciative of them for that. That’s probably the thing that gives us a chance to play this game on Thursday night: the guys doing a great job of that here in the building and at the game.”

The Ravens announced earlier Monday that “multiple members” of the organization had tested positive without providing details. The Athletic reported as many as four members of the organization tested positive, including staff and players.

“We will continue to work closely with and follow guidance from the NFL, team doctors and our medical trainers,” the Ravens said in a statement.

The Ravens, with their sudden shortage at running back, will face competitive issues against the Steelers. But the NFL does not appear to be considering a postponement of Thursday night’s game unless there are further positive tests by the Ravens.

Players, coaches and certain team staffers are tested daily under the protocols developed by the NFL and the NFL Players Association. The positive test results came from the game-day testing conducted Sunday before the Ravens played the Tennessee Titans in Baltimore.

The NFL has kept games on schedule after a small number of positive test results on a team. The league has had few disruptions to its schedule since enacting a protocol modification last month by which those identified as high-risk close contacts are placed in mandatory five-day quarantines.

The NFL completes Week 11 of its regular season with Monday night’s Los Angeles Rams-Tampa Bay Buccaneers game in Tampa. The league has had one widespread outbreak on a team, when 24 members of the Titans organization tested positive in late September and early October. That contributed to games being rescheduled in Weeks 4 and 5. The Titans played a rare Tuesday night game. But the NFL has made minimal scheduling changes since Week 5.

League leaders have said they would add a Week 18 to the schedule only if all games cannot be played in the current 17-week framework. NFL owners also ratified a proposal by the competition committee to add two teams to the playoff field, increasing it from 14 to 16, if the regular season is cut short by the pandemic.

NFL officials have said they know their task will only get more difficult in trying to complete the season, with caseloads spiking nationally and the holidays at hand. The league has made its intensive protocols applicable to all teams at all times for the remainder of the season. Those enhanced protocols, with increased mask-wearing requirements and bolstered distancing measures, previously applied only to those teams with positive cases and those exposed to the virus.

The NFL has said it has seen no evidence of on-field transmission of the virus from player to player or team to team during games.

The league also formed a committee of outside advisers before the season to assist Commissioner Roger Goodell on competitive decisions related to the coronavirus.

But mostly the NFL has had teams push forward even when they have been disadvantaged competitively by players being quarantined as high-risk close contacts. The Las Vegas Raiders had a significant number of defensive players unable to practice last week before they lost Sunday night to the visiting Kansas City Chiefs, although most of those players were eligible to play in the game. The Ravens faced a similar situation this season when seven defensive players were identified as close contacts to cornerback Marlon Humphrey after he tested positive.

Minnesota Vikings wide receiver Adam Thielen and Chicago Bears safety Eddie Jackson were placed on their teams’ covid-19 reserve lists Monday. That list is for players who test positive for the coronavirus and those identified through contact tracing as close contacts.

The Buffalo Bills announced that tight end Tommy Sweeney will miss the rest of the season after being found by a cardiologist to have myocarditis, an inflammatory heart condition that experts say has been found in some covid-19 patients. Sweeney had been sidelined by a foot injury and had been on the covid-19 reserve list, reportedly as a close contact.