The NFL has acknowledged a link between football and the degenerative brain disease CTE for the first time.
Jeff Miller, the NFL's senior vice president for health and safety, spoke about the connection during a congressional committee appearance on concussions on Monday.
During a discussion on whether there was a link between the sport and chronic traumatic encephalopathy (CTE), Mr Miller referenced the work of Boston University neuropathologist Dr Ann McKee, who has found CTE in the brains of 90 former pro football players.
"Well, certainly, Dr McKee's research shows that a number of retired NFL players were diagnosed with CTE, so the answer to that question is certainly 'yes', but there are also a number of questions that come with that," he said.
Democrat Representative Jan Schakowsky asked if there was a link between the two, and Mr Miller replied: "Yes. Sure."
The NFL has not previously linked playing football with the disease, which is linked to repeated brain trauma and associated with symptoms including memory loss, depression and progressive dementia.
It can only be detected after death.
Among players found to have CTE were Hall of Fame stars Junior Seau, Frank Gifford and Ken Stabler.
Last month, Dr Mitch Berger - who is a member of the NFL's head, neck and spine committee - said that while the types of degenerative changes to the brain associated with CTE have been found in former football players, they have also been found "in all spectrums of life".
He said that Tao, a protein which indicates the presence of the disease, "is found in brains that have traumatic injuries, whether it's from football, whether it's from car accidents, whether it's from gunshot wounds".
In the build up to Super Bowl 50 last month, Dr Berger would not draw a link between the sport and the disease.
The NFL agreed to pay damages to the families of those who were found to have the disease between 2006 and April last year in a 2015 settlement.
