No clue what happens behind the scenes with all the draft posturing and offseason "updates," but based on the injury the prognosis can't be good.
Location - "Navicular" is a less common type, but more common among "jumpers" (e.g., volleyball). It's basically at the hub of your foot (like "parietal" lobe of your brain) that in bball is constantly in use, torqued, and under stress.
Healing - "Navicular" is even vague, because multiple types of fractures could have occurred within that particular area. Beyond that, he could have all kinds of associated ancillary problems (e.g., tissue damage). Bone, tissue or nerve may have healed incorrectly the first time around, which could well be permanent; in contrast, if it just didn't heal, that could be a different issue...
Age - It's especially concerning b/c of his age. Given his history, physical size, and poor healing / break, it wouldn't be uncommon for him to have had injury / stress fracture to the navicular bone for a long period of time, as they commonly go unnoticed for years. If so, more untreated damage over a longer period of time... not good.
That said, I would consider sending off the 3 rooks for him.