Injuries stop greg playing on a high level maybe that is why he became what we called barney since he can't play on a pace that the gins play although he got rings, it could been a better career if he is not prone to injury, or maybe he might be mismanage during his career, its a tough match-up for JMF, sadly over the years he become slow and slower, they could have maximize him in the paint, add a fast pg, and sg for fast defense and let greg operate under on his pace.
Indeed, injuries really change the game play of a player, and same with what you said mismanage of his career, after having such injuries coach and conditioning asst coach will also change your game time, then rumors about his relationship with SMC management that really cause his career to pull down.
If by chance, CTC will sign him back and he start taking his conditioning seriously there's still something that they can pull from him, aside from his height his familiarity with his teammates and the game system, it's not going to be an easy path but if there's a will he can provide help both defense and offense still.