Miami Dolphins guard Richie Incognito's role in alleged harassment of teammate Jonathan Martin is under review by the NFL Players Association due to an incident that provoked Martin to leave the team, according to multiple sources.

One high-ranking Dolphins official who did not want to be identified defended Incognito as a player who has been a "model citizen" and was mystified by any allegations related to Incognito.

Meanwhile, several sources insisted Incognito was involved, adding that the incident was not isolated and extended to 2012, when Martin was a second-round draft pick by the team. One source said any emotional issues Martin is experiencing are directly related to his harassment.

An NFL spokesman said the league was monitoring the matter and has been in contact with the Dolphins since Martin left the team. On Friday, Dolphins coach Joe Philbin said, "This is something we take very seriously and will not be tolerated."

Union sources say the union will continue to conduct a thorough and detailed review that would extend to the team's workplace environment and affected players, noting the juxtaposition that it represents all NFL players, including Martin and Incognito.