What, exactly, is troubling about a running back who has torn knee ligaments in back-to-back seasons? Everything.

Marcus Lattimore is confident that he’ll pull an Adrian Peterson. The problem with that ambitious goal doesn’t just lie in his ability to have a fully functioning knee that allows him to be capable of cutting and juking, and do the things that explosive and elite running backs do. Those things are merely the foundation for the worry which surrounds the former Gamecock who dislocated his left knee, and tore several ligaments in a late October injury. What goes beyond that is also what makes the comparisons to Willis McGahee poor.

Lattimore is trying to be Peterson, but he’s only a year removed from another ligament tear in the other knee. Yet we really think he could be worth a third-round pick? Yes. Maybe.

Mike Mayock does, and anything Mike Mayock says between February and late April is generally treated as gospel. Without his most recent and most devastating knee injury, Lattimore easily would have been a first-round pick while challenging Alabama’s Eddie Lacy to be the first running back off the board. But Mayock still ranks Lattimore as a top five prospect at his position despite the injury, giving him a third-round grade. To compare, some recent running backs selected in the third round include Stevan Ridley (73rd overall in 2011), Shonn Greene (65th, 2009), and Jamaal Charles (73rd, 2008).

Greene sucks, but those other two guys are pretty good. At this point in late February, it’s difficult to imagine Lattimore even reaching Greene levels, let alone the production of Ridley and Charles.

Dr. James Andrews — the hippest surgeon in the land who turns knee ligaments into gold as he’s showered with gold — disagrees. Andrews told USA Today that Lattimore is three months ahead of schedule in his recovery, and he’s already gained 20 pounds of muscle.

“He’s twice as far along as we ever expected him to be. He’s so self motivated. This weight he’s put on has been all muscle, which is absolutely impossible in most cases. It remains to be seen if he can play this season. We’ve had to slow him down in certain activities because he’d get ahead of us. He’s one of the finest young men I’ve ever had the opportunity to help take care of.”

Unlike McGahee before him (he sat out a season on the PUP list after the Bills took him with their first-round pick, even though he also tore knee ligaments in his final college game), Lattimore has plans to play next fall, and he’ll run for scouts at South Carolina’s Pro day in April. That’s noble, but as Mayock notes, any team that drafts him realistically can’t expect a major impact until 2014. If it’s difficult to project how his recovery will progress now despite Andrews’ shiny words, looking ahead over a year is even more troubling.

That’s why right now for many, spending a third-round pick on Lattimore is difficult to justify. But just as we’ve noted multiple times regarding Robert Griffin III’s recovery and a year ago with Peyton Manning’s, there’s always an emphasis on two words in the preceding sentence: right now. No two recoveries are identical, and while the focus shines on the likes of Peterson and Charles from this past season and their highly successful recoveries, we forget about, say, Rashard Mendenhall, who struggled immensely after his own ACL tear. The result? The Steelers will let him walk as a free agent.

Mayock is basing his estimation on Lattimore’s evidently super human recovery, one that will presumably continue and have him prepared to make some kind of minimal contribution in 2013. But as former GM Charley Chasserley said, the various celestial bodies will have to align properly for Lattimore to be a third rounder.

“You have to see the medical diagnosis. The team that picks him is going to be one that doesn’t need him. You’re probably going to have a running back or depth at running back and you may be looking for a guy a year from now. “

If that depth is present, a running back who had 835 total yards on 4.9 yards per touch this past season despite playing in only nine games is worth the mid-round risk.