Martin left the Miami Dolphins last week and Incognito was later suspended in the incident. Martin, who was in his second season in the NFL, and Incognito, a ninth-year-pro, are both offensive linemen.
Incognito allegedly sent threatening email messages that included racist language. Several teammates have spoken in support of Incognito.
The NFL retained New York attorney Ted Wells to investigate the circumstances that led to Martin walking away from the Dolphins.
NFLPA Executive Director DeMaurice Smith issued a statement Thursday stating that he is looking forward to "information that defines the full scope of the NFL's investigation."
"Every NFL player should expect safe and professional working conditions," Smith's statement read. "The NFLPA has taken steps to ensure that every one of our affected members is represented. It is our duty as a union to learn the full facts, protect the interests of players involved and hold management accountable to the highest standards of fairness and transparency."