The repair of the lateral meniscus that tore off the bone when he suffered the injury in September is not the issue, according to several sources with direct knowledge of Jack's situation. Instead, the cartilage and bone have begun to separate, creating what is referred to by medical professionals as an osteochondral defect.
If or when the bone and cartilage fully separate, Jack will need to undergo another procedure and it will keep him out for a prolonged period of time. One possibility is microfracture surgery, though there are other options that teams have discussed.
Accordingly, teams that draft in the teens are now playing out scenarios in which Jack falls to them and they're considering the difficult question of "What will we do?"
There is confidence that a team in the mid-to-late teens will serve as a draft floor for Jack, so a fall out of the first round is unlikely. Jack believes this, and several sources believe the same.
But Jack's question marks could very well create a tumble out of the top 10.
Jack didn't run a 40-yard dash at his pro day on March 15, which led teams to begin digging into his medical evaluation. After NFL Scouting Combine rechecks earlier this month, the questions intensified. His agent, John Thornton, recently posted on Twitter a video of Jack working out, one where he looks healthy.
But as one GM told me: "It's not about if he's healthy now. It's about if he gets through his second contract."
Another top evaluator asked this question: "Is he a four-year player or a 10-year player? But technology is better now. So we really don't know."
No one questions what kind of player Jack is -- he's a rare talent. Teams are still trying to figure out how long he'll be that type of player.