The NFL hit back at a report claiming its committee omitted more than 100 cases of concussions from 1996-2001.
The league's foundational research, much of which laid the groundwork for its current concussion policies, was significantly flawed by omitting more than 100 diagnosed incidents of head trauma, the New York Times reported on Thursday.
A committee formed by the league in 1994 was tasked with determining, among other things, the scope of the NFL's concussion issue.
The Times report heavily criticises the study on multiple fronts in addition to the omissions.
A lack of transparency, conflict of interest and poor analysis led to faulty and misleading conclusions, it says.
The most damning allegation is the NFL severely miscalculated the rate of concussions, then downplayed the risk to players.
Troy Aikman and Steve Young, both of whom suffered multiple concussions during their playing careers, were cited as players diagnosed with severe injuries not included in the research done by the league's committee.
Another interesting element to the Times report is a connection between the NFL and Big Tobacco.
"Records show a long relationship between two businesses with little in common beyond the health risks associated with their products," the Times report read.
The NFL issued a response to the Times story later in the day, saying it is "contradicted by clear facts that refute both the thesis of the story and each of its allegations".
Much of the NFL's rebuttal focuses on the Big Tobacco link, but the league did say it never claimed to have studied every concussion suffered by an NFL player during the survey period.
Dallas Cowboys owner Jerry Jones said this week he was not convinced the data shows a link between CTE, a degenerative brain disease caused by repeated blows to the head, and playing football.
In 2013, the NFL settled its concussion lawsuit with a group of retired players for $765million.
The players alleged the league covered up the risk of concussions.
A number of players are appealing the settlement, and according to the Times, they are asking for an examination of the committee's research.