Each week, though, Slay said he prepared like he was going to return to the lineup.
It has happened twice since Mathis took over for him -- against Chicago when Mathis had a head injury and then again Sunday, when Mathis injured his groin and couldn’t return to the game.
Enter the rookie Slay, who has shown improvement in each of his fill-in appearances, including four defensive tackles and a special teams tackle Sunday.
“Rashean has done a nice job coming in and setting a good example for Slay,” Detroit coach Jim Schwartz said Monday. “I think Slay’s been improving over the last month. I think being able to sit back and watch a veteran player like Mathis has really been beneficial to him and I think you saw that when he went on the field.
“Physically, he’s done some good things but I think mentally and just game-awareness he continues to improve.”
That was a big issue for Slay early on, as opponents appeared to pick on him. And while he picked up a pass interference penalty Sunday against Cleveland while defending a pass to Greg Little, Schwartz was even fine with that.
“I thought he did a really nice job on that play,” Schwartz said. “Got a hand in. It got called, but I thought he made a nice play on the ball there.”
It is all part of the maturation process for Slay, who said last month he was going to try and learn everything he could from Mathis. Mathis, in turn, planned on tutoring the rookie because he saw he has a big future.
“They see that I am an approachable guy,” Mathis said last month. “I pull them aside before they can pull me aside and that lets them know I really do care about their future.
“As veteran guys, that’s what we have to do.”