(CNN) -- Former Penn State assistant football coach Mike McQueary, who testified that he saw Jerry Sandusky in a shower with an underage boy, filed a whistleblower lawsuit Tuesday against the university, according to a court document from Centre County, Pennsylvania.
McQueary was a key prosecution witness and was the only individual -- excluding the victims themselves -- who said he witnessed an apparent sexual encounter between Sandusky and a boy. Sandusky, who has maintained his innocence, was convicted in June for abusing young boys over a 15-year-period.
In support of McQueary's whistleblower claim, the lawsuit states he was the only assistant football coach who was not invited to interview for employment with the incoming new head football coach after longtime coach Joe Paterno was fired amid the Sandusky scandal.
McQueary also claims he was the only former employee who was not reimbursed for legal fees, and that he did not receive his severance payments on time.
The lawsuit states McQueary believes those situations and his employment termination were the result of his cooperation with authorities in the Sandusky case.
According to the lawsuit, after testifying in court, McQueary was placed on administrative leave with pay in November 2011, only to later be terminated in July 2012. A copy of a letter from the university athletics director concerning the administrative leave was filed along with the lawsuit.
Calls to McQueary's lawyer after the suit was filed were not returned.
Penn State University spokesman David La Torre responded to CNN with "no comment" regarding the suit.
According to the lawsuit, McQueary is seeking $4 million from the university as the equivalent to a total life-long salary as a football coach with the school.
CNN's Susan Candiotti contributed to this report.