That rookie wide receiver Amari Cooper simply wasn’t himself through much of the second half of the season was obvious to both the naked eye as well in the statistics.

Over the last five games of the season, the rookie first-round draft pick caught 14 passes for 219 yards — and most of that damage came in a six-catch, 120-yard effort against Green Bay.

General manager Reggie McKenzie told Sirius XM radio Monday night there were times Cooper was merely running routes to draw coverage his way.

“That hurt us at the end of the season. The last five games, people don’t know, Amari, he could hardly practice,” McKenzie said. “We held him out, he just could not do the things he could do early in the season because that foot was bothering him. He showed his toughness by playing every game. In some of the games he was just a decoy, but he gave it all he had.”

Other observations from McKenzie during a seven-minute interview included:

End of first wave of free agency

“We’re probably done with the big spending, yes, but there are always ways to improve your roster.”

The signing of guard Kelechi Osemele to huge money for a guard and what he brings

“He’s a guard that can play tackle, that’s just the added plus we have with him. He can play a lot of positions. During the course of a game, you need that … The bottom line is he’s a good football player and you’ve got to pay for the good football players. That’s just the way it goes. Any time you play in the free agency market, money is going to be involved, so you’ve just got to set you mind to it and that’s the way it is.”

The progression of quarterback Derek Carr

“Derek is going to get better year after year. I mean, he’s going to get better game after game. The thing about Derek, he wants to do so much, all the time . . . and he’s hard on himself. He’s one of those guys, if he relaxes, he’s going to be fine. His stats have gotten better Year 1 to Year 2, we’re hoping that it gets even much better in Year 2 to 3. We’re looking forward to Derek having a great year and carrying this team this year.”

Issues at running back

“I feel good about Latavius (Murray). We’re going to have to get healthy there. We were hurt with (Roy) Helu and Taiwan Jones. They both were hurt. So we’ve got to get healthy. We’ve got to get better there. Both our fullbacks can play running back, too, that helps, we’ve got Olawale and Marcel, he’ll miss the first (three) games, but those guys can step in and kind of run some power plays. We have some guys, you always want to create competition, you never just let a good player go by. If somebody wants to cut one, then I’ll claim him.”

Whether Bruce Irvin and Khalil Mack are interchangeable

“No question. Those guys got the size, they got he speed, and Bruce is not a power player that Khalil Mack can be, but Bruce can do multiple things and our coaching staff will put him in position to make plays, and that’s where we’re all looking forward to that.”

Irvin’s position — outside linebacker or defensive end

“I think he’s a linebacker. He’s an outside linebacker that can play defensive end whenever you need him to. He’s too athletic and fast to not put him at linebacker and at least let him roam around and do some things. He can cover, he can run. He can do many things they’re excited to figure out how they’re going to use him in many ways. It’s going to be fun to watch.”

Thoughts on bringing back Aldon Smith

“The first thing is we want Aldon to take care of Aldon and that’s my first order of business. I’m not worried about re-signing him until he gets himself together, then we’re going to talk. I want Aldon to take the right steps that he needs to do to get his life in order and get back mentally ready.”

What cornerback Sean Smith brings to the defense

“Two things, he brings valuable experience and he brings a skill set. With his size and length and ability to cover, especially the way we play our corners, he’s going to fit right in. So it’s just a right fit, I mean, it was perfect for what we do. Him being available for us to sign, that was gravy, that was gravy for us.”

The continuity of the staff and the team growing with it

“I see it as going nothing but up. Any time you keep the staff together, and they’ve been through it. they’ve been through it with new players, and now they know these guys and they know each other better after going through it. I see much improved football team going into 2016. They’re hard workers, they work well together. I think the sky’s the limit.”