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The NFL and NFLPA formally began their investigation into the Titans' COVID-19 outbreak on Friday, with officials from both sides in Nashville amid concern about several potential breaches of protocol, according to sources with knowledge of the situation.

The NFL began drawing data from contact tracing and all available sources on Tuesday when a host of positive test results began, with a total of eight players and staff among that initial group. Numerous sources who have been in contact with high-ranking NFL officials said that there were already concerns arising from the immediate data about potential infractions, with an expectation among other team executives who have been in contact with league officials that significant penalties could be forthcoming for the Titans.

Specifically, the investigation is looking to determine if there were any violations of protocol regarding the intake of defensive back Greg Mabin, who was signed to the team's practice squad on Thursday and would later test positive for COVID-19 two days later. Sources said that the initial review of contract tracing indicated early in the week that this is when the virus entered the team facility.

Subsequently, given how the virus spread among both coaches and players -- initially on the defensive side of the ball -- there are also concerns that given contact tracing data outside linebackers coach Shane Bowen, who tested positive on Saturday, perhaps should not have been the only member of the staff not to travel with the team for the game in Minnesota. By Tuesday's outbreak the NFL was already expanding the scope of its probe, requesting practice video and other materials to continue to gather information as to whether or not PPEs and facemasks were being used as per the protocols both in that facility and on the practice fields.

"Make no mistake, this is not an inquiry -- it's an investigation," said a source with knowledge of the situation. "Was this preventable? Was this manageable? That's where this is going. It would be fair to say there are some troubling signs on a multitude of levels ... The violations aren't just happening there -- just look at what you see on team feeds on social media -- but there is obviously heightened concern about this situation."

Head coach Mike Vrabel said repeatedly in his remarks to the media last week that the team has diligently applied every aspect of the protocols and regulations throughout this process. "We're following the 100 (COVID-19) memos (the NFL) sent out," Vrabel said when addressing the matter with reporters. Some in the league office are concerned that management and ownership have not addressed the situation in a more public manner as well.

"Their building is on fire," said another league source. "Were they doing everything possible to put it out?"

The NFL hopes to play the Steelers-Titans game in Week 7, but that remains in doubt as long as the team's facility is closed. Three more positive tests came out of the Titans player and staff pool on Saturday and, while there is not an exact timeframe in place, league officials have said they would likely wait for a few days of no new positive tests before reopening a facility.

The league has also said it believes for competitive balance and health and safety reasons, a team should be allowed to have at least two practices at their facility before playing a game that week. While the Steelers coaches and officials have said all the right things in the media this week, sources said they will be watching the results of this investigation very closely, with the expectation that if any impropriety took place that very strong punishment should follow. Pittsburgh, like the Titans, went on the bye this weekend and now faces the prospect of playing 13 straight games.