On Thursday afternoon, San Francisco 49ers defensive coordinator Robert Saleh shared his theory on why rookie linebacker Reuben Foster tends to get shaken up during games.

Outside of two injuries earlier in the season that forced the hard-hitting defensive player to miss six games, Foster has always returned to the field relatively quickly, usually only missing a snap or two. This past Sunday against the Tennessee Titans, Foster missed two snaps due to a neck stinger.

Saleh believes Foster's playing style might be the reason for the trend.

"He hits the daylights out of people," Saleh said. "Every once in a while, he's going to get something where he might have to take a breather. It's been a while since I've seen someone who hits as hard as he does. I think after a full offseason where he can just build his body instead of having to rehab, eat right and do things the right way, I think he'll avoid some of those injuries as he gets smarter in the game."

Foster has started the 49ers' last six games. During that time, he has been credited with 54 combined tackles. Foster's rookie season has been so impressive that he was named the Defensive Rookie of the Month for November, which was his first complete month on the field.

On Thursday night, head coach Kyle Shanahan joined KNBR and discussed the same topic. He was asked if the coaching staff had any concerns about Foster's violent playing style contributing to injuries.

"There's always concern, especially when you play that way," Shanahan said on the "Tolbert & Lund" show. "But that's also what makes him great. That's not something you want to take away from him, but it's something that I think he has to be very aware of, especially going into the offseason, especially as he gets older.

"You can't just go out there and play that way and just show up and not fully take care of your body. And that's not just going to be an in-season thing for him. It's going to be a year-round thing.

"He's going to have to come into the next offseason in the best shape of his life. He's going to have to eat right. He's going to have to sleep well. And you're going to have to recover throughout the week during games and take care of your body. Because all players have to be that way, but especially when you're a linebacker, especially when you play the way he does. I think it's going to be even more important."

You can listen to the entire interview with Shanahan below.