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."

Richie Incognito's role in alleged harassment of Jonathan Martin is under review by the NFLPA, according to sources. AP Photo/Tom DiPace

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.

Nevertheless, sources say NFLPA attorneys already have gathered numerous details relating to the allegations that identify Incognito prominently as one of the offenders. Incognito was not available for comment, and Philbin did not mention the veteran as an alleged culprit.

Incognito suffered a neck injury in Thursday night's win against the Bengals, a game that was missed by Martin, who also was unavailable for immediate comment. Philbin gave the team Friday off.

Martin's goal is to return to the team, sources said, but no projected date was provided. The team resumes practice Monday and has until Tuesday at 4 p.m. ET to keep Martin on the roster or place him on the non-football illness list.

The Dolphins have not said much about Martin, except that he has been excused with a non-football illness and that they are concerned about him and supporting him.