ANN ARBOR, Mich. – Detroit Lions wide receiver Calvin Johnson is contemplating retirement after nine NFL seasons, but at least one opposing NFL head coach doesn’t want to see him go.

“Yeah, I don’t know. I hope he doesn’t retire,” Baltimore Ravens coach John Harbaugh said before the University of Michigan’s "Signing of the Stars" event Wednesday. He is here in support of his brother, Jim, the Wolverines' coach. “I hope he keeps playing, mainly because we don’t play the Lions next season.

“If we play him in the Super Bowl that would be OK. I can live with it. But I’m a big Jim Caldwell fan obviously and love those guys over there. It would be tough. It would be a sad day for the league if he retires.”

Even opposing coaches don't want Calvin Johnson to retire, though that's a little easier for an AFC coach to say. AP Photo/Duane Burleson

On Sunday, ESPN Insider Adam Schefter reported that Johnson told Caldwell that the 2015 season would be his last after the team’s final game. Schefter also reported Johnson confided in quarterback Matthew Stafford and linebacker Stephen Tulloch that 2015 would be his final season.

Johnson has played in 135 games and posted 731 receptions for 11,619 yards and 83 touchdowns. He holds 15 NFL records and almost every significant Lions receiving record.

If he follows through on retirement, he would be the latest NFL player hanging it up close to his prime, joining Barry Sanders, Patrick Willis, Jim Brown and others. Harbaugh is not concerned about early retirement becoming a trend, though.

“I think that’s all personal. You can go all the way back to Jim Brown, he retired after nine years at the peak of his career,” Harbaugh said. “That’s always going to be a personal choice, a personal decision people are going to make.

“You wish everybody well whatever they do.”

At least one of the NFL players in attendance, though, understands why Johnson might consider retiring. Especially since Tennessee Titans defensive tackle Mike Martin grew up watching the Lions and Johnson in suburban Detroit.

“The guy, he’s made a lot of money. He doesn’t have to worry about it on that end,” Martin said. “You get to the point in your career where you can retire and not have to worry about the amount of money you made and be comfortable, that’s a nice perk. He has that perk.

“Also, from his standpoint of the Lions organization, they haven’t been doing too great. As a player in his position, because you want to win, you don’t want to come back and just make money. It’s not about that. It’s about winning at the end of the day. Everybody wants to win.

"I definitely see where he’s coming from.”

Beyond a statement saying he was evaluating his options, Johnson has not said anything about his plans or why he has been considering retirement. ESPN Insider Ed Werder said it is because Johnson is concerned about his long-term health.

Johnson has had ankle, knee and finger injuries the past three seasons.