(ABCNews)-- Brett Favre has become the latest former National Football League player to reveal he is suffering memory problems after spending 20 years on the playing field.
On ESPN Radio the former star quarterback said that he had become worried about the state of his memory in recent years.
"I think after 20 years God only knows the toll," said Favre, who was sacked 525 times, more than any other NFL quarterback. "This was a little shocking to me, that I couldn't remember my daughter playing youth soccer."
New research about the effect of repeated head injuries on pro-football players has only recently revealed how devastating the longterm toll can be. As a result, the NFL has come under fire for putting players in unsafe conditions.
Of the 34 former NFL players who have died and donated their brains to research, the percentage of them who have pathologically confirmed chronic traumatic encephalopathy (CTE), a degenerative brain disease, is over 90 percent, according to a 2009 University of Michigan report.
In August the league paid $765 million to players and their families who sued the league over head injuries that they blamed on their time playing pro football.
There is no data on how many hits it takes to bring on symptoms of CTE, but experts caution no head injury is safe.
"There is still a pervasive belief that only a concussion serious enough to knock the athlete out will do damage, but that's not the case," Harvard neurologist, Dr. Marie Pasinski. "Any blow to the head that leaves a person slightly dazed or not quite right may cause harm to the brain."
There's no proof that Favre is suffering from CTE, which can only be diagnosed after death.
However, patients with CTE display symptoms "such as impulsivity, forgetfulness, depression, [and] sometimes suicidal ideation," according to Dr. Russell Lonser, chairman of the Department of Neurological Surgery at Ohio State University.
Favre's admission about his memory came just days after the St. Louis Rams called the retired quarterback to see if would return to the field and play for the team. Favre, 44, retired from the sport in 2010.
"I want to live a long time, I want to live healthy, as close to normal life as I can," said Favre.
ABC News' Liz Neporent contributed to this report.