How good could Michael Crabtree be? It’s a question most of us have stopped asking, figuring the answer lies in the numbers. Crabtree’s averaged about 750 yards and 4 touchdowns per season. He’s a decent blocker, and he doesn’t particularly like training camp. He’s good for a few great catches as well as at least a half dozen drops a season.

He’s a good No. 2, but the 49ers need to look elsewhere if they want a receiver who’s a weekly threat against No. 1 corners and double-teams.

Leave it to Jerry Rice, who talked to reporters including Cam Inman and Ron Kroichick to promote a Nationwide Tour event today, to expect more (much more) from the 49ers’ wide receiver.

Are you watching on TV to see how Crabtree runs his routes?

“That was something I was always looking for, and I just did not see separation. A lot of times, as route runners, you’re always going to see that separation when a quarterback has no hesitation (and) he knows where he wants to go with the ball. That’s something I didn’t see from the 49ers. Maybe that’s part of the game he needs to work on, getting that separation. I was always one of those guys, even though you have receivers big and fast now, I felt I had to be at a certain weight to get my quickness. I don’t know exactly what he weighs. He could lose maybe 10 or 15 pounds and be more explosive.”

What did you play at?

“I played at 189 (pounds), 190, 200. I always wanted to change, and to be able to control that, there were sacrifices you had to make. When I was at 189 or 190, I felt I could run all day. My thing was about wearing an opponent out. By the fourth quarter, I was always at my best.”

Could Crabtree be that explosive guy?

“Yeah but that’ll be up to him to make that decision. You have to sacrifice yourself and put your team’s best interest at heart. I don’t really know the guy so I can’t really comment on his work ethic. They feel there’s potential there but it’ll be up to him to say, ‘I want to be the best receiver I have to be and I’m going to have to sacrifice some things.”

Ouch. As if Crabtree didn’t have enough crap to deal with, with people in matriarchal basements from Eureka to San Luis Obispo calling for the 49ers to add a wide receiver — any wide receiver — who’s better than Crabtree. And that’s when he isn’t fending off kids going the “Hey Mister” route, in hopes Crabtree will buy them a little Four Loko.

Now with the best receiver in NFL history calling out Crabtree in a similar way to how Brian Sabean and Bruce Bochy threw Aubrey Huff under the bus for his lack of conditioning at the end of the 2011 season, Crabtree’s going to have to answer critics who wonder if Rice has a point. Does Crabtree do all he can to be the best, most explosive wideout he can be? Or does all that time missed during training camps point to the personality of someone who doesn’t spend every spare minute running up steep hills in San Carlos?

I remember during Rice’s playing days exactly what he spoke of, how he was always tinkering with his weight. He’d shave 10 pounds to get a little extra burst. Then he’d come in with 15 pounds of muscle so he could take more punishment. Rice had a little Mad Scientist in him, and worked on his own body almost like a mechanic.

Whether or not Crabtree is the same way is hard to tell. He’s a private person, not all that forthcoming with the media, and judging from these comments from Rice, Crabtree probably doesn’t give the Hall of Famer regular weight updates.

You were with him in Dallas before the draft with Deion, but you never got to know him?

“I never did. Maybe because I voiced out and made a comment about Crabtree when he was holding out, and I said he needs to be in there sweating it out with his teammates and let everything else work out. I think ever since then he got offended.”

But he’s a quiet guy, too, so …

“He’s a little bit different. I never to come in between a man and his money. But I felt he needed to be in there with his team. I voiced that, and after that I could tell he would look at me in a certain way.”

He’s never played in an exhibition game.

“Would I be surprised that happened again this year? I wouldn’t. Maybe he feels he doesn’t need to play in the preseason. I looked at preseason as a time to gel with my quarterbacks and teammates, being out there on those hot days and going through it with those guys. I always tried to better myself in training camp and that threw me into the regular season ready to go. I’d have everything sharpened up.”

Like it or not, since Rice was the one pointing one of his massive fingers at a problem most didn’t even consider, Crabtree’s going to have to answer questions about this. While Crabtree’s never seemed like he was on his way to nearly eating himself out of the league like Mike Williams, he’s not a player who’s going to dominate with size and strength. He isn’t small, but he’s also in that “possession receiver” category when it comes to speed.

If Rice’s comments lead to an increased commitment to fitness and a little more time running with his teammates during training camp, perhaps old Flash 80 gave his old team an unexpected boost — one Trent Baalke and Jim Harbaugh will thank him for privately.

Then again…

Rice also had this to say about whether or not the 49ers should go after Peyton Manning. Cover your eyes, Alex Smith!

Quarterback wise, you want them to go with Manning?

“If they’re going to invest that much money in Alex and they feel he can get the job done, then do it. I know he made significant improvement this year and did what was asked of him. If he can get more weapons around him and knowing he has a coach that has confidence in him, that he doesn’t have to look over his shoulder, it might bring the best out of him.”

Would you make a push for Manning?

“I would. If he’s a free agent. I think you go for it. A guy of that talent, you’ve got everything in place. You’ve got a defense that smacks you in the mouth. You just need a little more out of the offense. That’s not knocking what Alex did. (Manning) can take you to a whole different level.

“If he goes to the Washington Redskins, and him going there, I guarantee they win 10 games. If he goes to Miami, they win 10 games.  And I know what you’re going to say: ‘If he’s healthy … ’

“If he’s healthy, he’s going to have a chip on his shoulder and he’s going to be pissed.”

“Harbaugh might be looking at this totally different.”

 Do you think the 49ers will go after Manning?

“Business is business. You have to.”

It looks like Manning’s available.