Free agents with low overall ratings are eventually pruned from the free agent pool. If he's happened to decline quickly and not been re-signed, chance are that's what happened to him. Or as Fitzy said, he could be on the injured list and you've just passed over him him looking through the rosters.
I noticed that aswell,except it seems that some players are not in the game at all such a s Tony Bobitt from LAL for example. I just can't find this guy but he's not the only one missing.
Such a pain when you're trying to update rosters manually.