The NFL and the NFL Players Association are investigating whether the Tennessee Titans, who have had 18 members of their organization test positive for COVID-19 in the past week, violated the league's virus-related protocols, sources tell ESPN.

After the Titans' recent outbreak -- during which nine players and nine team personnel members have tested positive, one source observed to ESPN that "This isn't a failure of the protocols; it is a failure to follow the protocols."

Officials from both the NFL and NFLPA have been in Tennessee since Friday, seeking answers to an issue that some sources believe ultimately will wind up with league making an example of the Titans.

The NFL and NFLPA have asked the Titans to turn over multiple videotapes of team activities so they can get a better idea of the root of the outbreak, according to sources.

The Titans are convinced, however, that they have obeyed the rules and have gone out of their way to protect their organization, a team source told ESPN. The Titans believe they have done everything the league has asked, have told the players to wear their masks and have been compliant, according to the source. The Titans also think they've done a better job observing the protocols than other teams around the league, the source said.

The Titans had two more positive tests come back Sunday morning -- one player and one coach, sources told ESPN, increasing their total to 18 members of the organization.

Eight players this week, and 10 overall this season -- defensive lineman Jeffery Simmons, offensive tackle Isaiah Wilson, linebacker Kamalei Correa, cornerback Kristian Fulton, wide receiver Adam Humphries, defensive lineman DaQuan Jones, long snapper Beau Brinkley, wide receiver Cameron Batson, tight end Tommy Hudson and cornerback Greg Mabin -- have been placed on the Reserve/COVID-19 list.

The investigation is focused on Titans outside linebackers coach Shane Bowen being the first in the organization to contract the virus, and a potential failure by at least some to report symptoms and wear masks. One source told ESPN that he suspects that this spread started with the Titans coaching staff.

Bowen was exposed to individuals who had been exposed to the virus, according to a source. NFL employees are required to report being around anyone who has contracted the virus or to not go into work if they are around those individuals.

If the NFL and NFLPA find that at least one member of the Titans didn't properly report being around someone or others with the virus, it would be a violation.

But there also is a sense from sources that the Titans were not diligent about wearing masks around their training facility, despite the protocols the league and the NFLPA have outlined in their memos. This could lead to the Titans facing discipline in the form of fines and or even a potential loss of a draft pick, according to sources.

The NFL announced Thursday that the Titans' game against the Pittsburgh Steelers would not be played during Week 4 because of the positive virus tests. The Titans are now scheduled to play the Steelers in Week 7 on Oct. 25.