ALLEN PARK, Mich. -- Rashean Mathis Jr. is 3 years old. This year, for the first time, he understands his father’s profession. Daddy is a football player. Daddy hits people for a living.

Daddy is Rashean Mathis, the 35-year-old Detroit Lions cornerback. When Mathis heard his son say "I want to play football" this year, those five words concerned Mathis more than any hit he has taken or delivered.

Mathis has pictures of his son on the field with his helmet following a big win against New Orleans in 2014; "moments that will last forever." His wife, Ebony, wanted Rashean Jr. to remember his dad as a football player. But Mathis wants his son to do anything -- anything -- other than football.

This is one of the lines Mathis walks as someone who understands the impact of brain injuries on football players. It’s something he understands with more clarity after suffering his first diagnosed concussion in the NFL in mid-October. The concussion wasn’t diagnosed for a week after the hit and landed him on injured reserve.

Rashean Jr. looks up to his father, and observes more of his habits than he did before. Mathis worries about his son's health and his own future. During offseasons in Jacksonville, Florida, he will try every sport with Rashean Jr. in an effort to keep him from the game that made Mathis rich.

"He’s a kid, and I have time to brainwash him in the offseason with golf," Mathis said. "So it balances out."

Mathis said recently that the injury is making him consider his future in a different way. He said he was unsure whether he would play next season, though he’s under contract with the Lions through 2016.

"Something like this happens, yeah, as a professional, I’ll be naïve to not think about those types of things," he said. "There’s life after football and you’ve got to think about those things."

He said he and the Lions decided to put him on injured reserve because they didn’t want him to return this season and potentially suffer another concussion -- or something worse.

Mathis played football as a way to improve his life and said he would do it again. Despite reading countless stories about what playing football potentially does to the brain, prior to suffering the concussion he said he would let Rashean Jr. play high school football if he really wants to compete. But not until then.

By that time, Mathis will have introduced his son to other sports, including golf, baseball, basketball and soccer. It’s similar to the message from NBA star LeBron James, who told ESPN last year he wouldn’t let his kids play football until high school, when they could fully understand "how demanding the game is."

"As a father I would have to take that stance," Mathis said. "If I’m protecting him from everything, then he’s not going to learn and grow in anything. But my stance on it, from the youngest age that I can, I would try to hinder him from playing it.

"But when it’s his time to make a decision, I would think I would have laid a solid enough foundation to say you have other options. Your choice to choose."

Mathis hopes his son chooses against football.

Mathis' research about football and brain injuries started after an National Football League Players Association meeting years ago. Now, he thinks everyone involved in the NFL can do better with player education.

Not enough NFL players, he said, really know about the dangers of their sport.

"Probably not so much as people would think, and that’s us as players, us as the PA, us as owners, us as organizations dropping the ball on it," Mathis said. "It has to be taken personally as well, and the player has to take more responsibility than anyone else to heighten his awareness on what, exactly, is going on and what might be going on and what’s really going on."

Mathis watched "League of Denial," the PBS-broadcast documentary on brain injuries in the NFL. He read published studies, including September’s "Frontline" report that revealed 87 of 91 deceased NFL players' brains came back positive for chronic traumatic encephalopathy (CTE). That number rises to 131 of 165 brains of football players studied by Boston University. He watched the "Real Sports" story on what CTE has done to former football players, and that’s when it hit home.

"You see guys that it’s affected, that CTE has affected and has affected tremendously, and the thought that this could be a reality is almost like ... this can’t be a reality for me," Mathis said. "It’s a double-edged sword because you think that, 'OK, this can’t be my reality.'

"But at the same time you couldn’t be naïve and say that, 'OK, how can’t this be your reality when this same person did exactly what you’re doing.'"

Mathis said until studies prove differently, until the rest of the world has CTE at the same rate as football players, he will relate football to CTE. He can’t not think so.

Despite his knowledge, Mathis said he rarely discusses it in the Lions locker room. He will remind cornerback Darius Slay to keep his head up when tackling to prevent possible head and neck injuries, but he said brain injuries are not discussed among players.

"How can you, in a world where this is your job and this is how you feed your family?" he said. "How can something that could stop you from playing this game, how could it be talked about without having an effect on how you treat your job. That’s reality."

The average NFL career lasts fewer than four seasons. Players are cut daily or given injury settlements. The adage of "the best ability is sometimes availability" fits. For all the NFL has done to diagnose concussions during games, players need to report a potential injury if they are noticing symptoms and haven’t been flagged. Sometimes players lie or ignore symptoms in key games, like former Lions tight end Dorin Dickerson did against the Giants in 2013.

Most guys are playing with their careers in tenuous positions, and that makes it difficult.

"It’s impossible right now," Mathis said. "Like I said, it has a lot to do with parents letting a kid know how important their health is, their brain is. But as of this day and age, being we weren’t taught that, it’s like, 'OK, this is my livelihood. This is how I feed my family. If I don’t play, I might not stay on this team.'"

Mathis believes this will eventually change. Locker rooms 10, 15 years from now could discuss CTE because the available knowledge should increase -- much like it has from Mathis’ rookie year in 2003 to now.

That’s the key. He thinks NFL players speaking about the realities of playing in the league could help future generations -- even if few do right now.

"It starts with more players being knowledgeable about it first or wanting the knowledge first. We should speak out about it, because it’s going to affect our kids. It’s going to affect other people’s kids," Mathis said. "It might affect your way of life one day to be like, 'OK, I was aware of it and these are the things that I was aware of and knew could have an impact on my life.'"

He said he learned more by going through it firsthand over the past month, adding that there is so much out there yet to be discovered about the brain, brain injuries and concussions. This, he said, makes the subject hard for players to research since so much of the information is evolving.

"We do know that it is affecting us," Mathis said in a text message. "How bad, how much, that's the kicker. And being that we know it does have an impact on guys' futures, there shouldn't be any limit of money or research dumped into this."

Mathis said he doesn't believe anyone is hiding anything, but he thinks everyone should be more up front and vocal about the impact concussions have on the lives of players and their families. Give them the research available and then allow them to make their own decisions.

The accountability for knowledge has to be on everyone: the NFL, individual franchises, coaching staffs, youth football and players themselves. This is why he’s speaking up. He doesn’t react to big hits when he sees them. He pays attention to what happens after.

He said players should take the lead in learning and understanding for themselves.

"[Are] the right precautions being taken after it happens? Because you can’t stop it. It’s impossible to stop. The thing about it, how does it affect the person and how long does it affect the person, is the concern and where I think we need to go," Mathis said. "We don’t need to go, 'Is it affecting them?' Of course it’s going to affect someone.

"How it’s affecting them and how long it’s affecting this person, that’s where we need to start shedding more light ... instead of saying, 'Oh, it doesn’t, our game is not, our game is concussion-free,' you know what I’m saying? But how much damage is it actually doing? That’s where it needs to go."

And that’s what more players, Mathis said, need to know.

Mathis has a vision. He’s 70, potentially finishing his second career as a professional golfer. He’s on the course, hopefully with his son. And he’s walking it. No limp. No golf cart.

Golf the way it was meant to be played, walking from shot to shot. This is still the future he envisions for himself and his son. But he also realizes he can do something to help protect and inform future generations.

When Mathis dies, he will donate his brain to research to see how football might have affected it.

"It’s not in my will yet, but I’m sure it will be," Mathis said. "If you can do anything after, it’s kind of like donating your organs after death. Why wouldn’t you if they are healthy enough to help someone else live or make life better?

"I don’t understand why you wouldn’t do something that could possibly actually make someone’s life better. That’s just me ... that’s just how I think mentally."