The secondary
The wide receiver room would be fair here. That's another question mark. Yet, with better play from the quarterback, the receivers will be better.
Donaven McCulley has proven he can produce in the Big Ten. Semaj Morgan and Fred Moore can play, too, as long as they have someone to get them the ball.
Underwood can do more than that. So let's focus on the one thing that's worrying about the defense. Michigan's front seven might be the best in college football. The defensive line might not be able to beat Ohio State nearly by itself, as it did last season, but it will be dominant.
The defense will be the defense from the bowl game, only it could be even better. The secondary will be the tipping point. Cornerback depth is a concern. We haven't seen Jyaire Hill play like CB1 for an entire season. Zeke Berry is a solid No. 2 but there isn't a clear cut third option.
There are also questions about when Rod Moore will return. It feels like in one of the first few games, but will he be as effective? It's going to take some time. I wouldn't bet against him, though.
At cornerback, ShamarI Earls and Jo'Ziah Edmond are each candidates to emerge. Caleb Anderson is another. But there are still some things to sort out. If the secondary is a strength, though, which it can be, this will be the best defense in college football.