I had a player miss the first third of the season with an injury. He's got a Durability rating that would require him to take the occasional day off throughout the course of a 162 game season. Does the missed time mean he could probably play everyday for the rest of the season and not get worn down?  Or does it prorate that kind of thing? 

Whenever I've had a player like that go on the 15-day DL, he's been good to go for the rest of the season without tiring.  I don't recall any of those injuries being from the start of the season though, so there might be some other mechanism at work there as opposed to the middle of the season, but I would think your guy would probably be OK.