Image updated to elaborate on his current skills on the defensive side.
A chef shouldn't be burning toast.
Seriously, how can people know he's toast when he hasn't played in so long and when he did he was batting injuries?
Good question. Can you trust the judgment of NBA coaches? GMís?
I myself havenít seen him even play in an NBA game in a long time, so Iím only going on what teams think of him; and while I have a high opinion of my own scouting prowess (!), NBA teams actually do pretty much know what theyíre doing. There doesnít appear to be any kind of market for him, and the Knicks simply gave up and paid him to go away. New York stretched him after taking a look this October, so they, at least, donít think that he could even make their roster. So itís likely, as I said before, that he doesnít have a lot to offer at this point.
He would have to replace someone else if he signed with the Celtics, so it doesnít make sense to bring him in for his wisdom and experience, or whatever. Boston has several bigs that can contribute now or have potential, given development; so I put the chances of this happening at zero.