Matthew Stafford could see how the NFL was wearing on Calvin Johnson.

"Not to say that I expected it, but I wasn't shocked," Stafford said, via the Detroit Free Press. "I've known Calvin for seven years and know the effort and the attitude that he plays with, and it takes a toll on people. And he was catching quite a few passes and getting hit quite a bunch, and so it takes a toll. And he's a guy that from an offensive standpoint was touching the ball or carrying the ball just as much as anybody. So I knew the NFL was kind of wearing on him and I just told him, when he told me he was done, I just told him, 'I'm happy for you if you're happy.' And that's what you want. He's a guy that gave everything to the game and you want him to be able to walk out on his own terms and feel like he did the right thing."

Stafford admitted duplicating Johnson's explosiveness and production would be difficult.

"It'll look different, obviously," Stafford said. "He was a player that drew a bunch of attention, not only in the red zone but all over the field. He was a guy that led that receiver group, showed those guys what it was like to work and what it was like to try and dominate a game, take over a game. We have obviously replaced with some pieces. No one player is going to replace a guy like that, but I'm confident in our coaches and our players that we have on our team, we're going to be fine."