Looks like the injury bug has hit a position with very little depth for OSU. Tommy Schutt was looking to be their starter at one of the DT positions (link says he was a backup at both, but I'm not sure I really believe that, he was going to play significantly and probably eventually start). They have little depth around him and almost no experience even with him. Going into the season, DT was probably their biggest concern, even more than an OL with serious depth issues. Well, that situation just got worse.
The OOC schedule is still easy, but teams like Wisconson, NW, Iowa, and PSU are the first four up in B1G play. Even when Schutt comes back he's unlikely to be 100%. While OSU has playmakers in the back end and in the pass rush, their lack of experience in the middle made them potentially weak against the run. Against the B1G teams listed above you don't want to be weak against the run. Wisconsin could pull out a big victory; NW, while being more of an outside run team, could potentially get OL to the LB level; Iowa is still good at blocking in the interior and with a few lucky bounces could be in a game they have no business being in; and PSU may be able to run the ball to take some pressure off their young QBs.
I still wouldn't expect many loses from that group of games, because the offense is still the offense. But this gives teams a chance and likely makes victory that much harder for the Buckeyes. Hate to see injuries regardless, but this is a big one for OSU.