Injuries have thrust San Francisco 49ers rookie safety Adrian Colbert into the starting lineup this season. With the perceived depth the 49ers once had at safety and the emergence of other young players during the offseason, Colbert, who was a seventh-round pick, was not a lock to even make the 53-man roster. Now, he is a featured player on the 49ers defense.

Colbert has played in 145 defensive snaps this season, according to Pro Football Focus, with his snap numbers gradually increasing over the past three weeks. That total is just a fraction compared to Jaquiski Tartt (595) and Jimmie Ward's (429) snap counts. Of course, both of those veteran safeties are now done for the season after each suffered a broken arm. On Sunday, against the New York Giants, Colbert is set to make his first career NFL start.

On Thursday, 49ers defensive coordinator Robert Saleh spoke to reporters about his young safety and shared what makes him so special.

"He's relentless in his work ethic and his preparation," Saleh said. "I love the way he hits. He's a very physical football player, and it's very important to him. I don't know if it's a chip (on his shoulder) as much as it is important where every rep, every play, every meeting, is very, very important. He's very into it, and he has something to prove, for sure."

While Colbert brings a great work ethic and physicality to the 49ers defense, Saleh believes the rookie needs to improve in one other area.

"He's got great range in the middle of the field," Saleh said. "He's got what I'll call -- professional -- he's a professional safety. He's a professional football player in that he can go red line to red line and cover ... It just shows that he is an NFL-caliber safety. His tracking angles in space when that ball does reach that second level -- we call him the eraser to erase all the issues that might happen in the run game -- he has the ability to track in space which makes him a really good special teams player.

"Now, the last part that we're trying to get to is mental. If he can get to that mental speed, we feel like he might be able to be a pretty good safety. But that's the last part of it."

The 49ers originally intended to use Colbert as a cornerback because of need and perceived fit. Once he moved to safety, the rookie began to shine, and the coaching staff quickly took notice.

"We knew the speed; we know the physicality (coming out of college)," Saleh said. "We knew that he was a really good tackler and all that stuff. So we did have him at corner, initially, just because of the way the roster had panned out when we had first gotten him. When he had his opportunity to go play safety, we were able to see some of the things that he was able to do, some of the things that we like out of a free safety. Leaving him in that spot and giving him a chance to go play it, it's kind of; I guess you could say, 'evolved.'"

Colbert has 13 combined tackles and a pass defensed this season. He owns Pro Football Focus' highest run defense grade among 49ers safeties and the third-highest among the team's defensive backs.