That to me is a problem with the player not the organization or medical staff. Maybe even from his teammates from not getting on him more. But seriously we've been listening to these excuses since pre-preseason. It's getting old.
When his knee is swelling, though, that's not all in his head, right? That's something that is medically observable, and cause for concern. It's not like he's faking it.
Also, keep in mind that one of the players the Celtics organization "called out" in the past was Big Al, for not recovering more quickly. The team suggested that Big Al's injury was all in his head... only to find that team doctors had misdiagnosed bone chips in his ankle.
Sometimes, players know their own body, and it does more harm than good to push through injury. Arguably, this is what happened with JO, when he played through obvious injuries with the Pacers, and it's likely that he's still feeling the effects of those decisions today.