I don't like the sound of this:

It's really sore," Sheets said. "It's kind of up in that region, top of the triceps and near the lat that I injured a couple years ago.

"It's hard coaxing yourself through it, especially with me tearing it once before. I'm cautiously optimistic about how it feels tomorrow."

Sheets said the triceps felt better each day leading up to his start Friday, but that going into it, he was still hurting. It really flared up in the third inning during an at-bat by opposing pitcher Bronson Arroyo.

"That's when it felt the worst," Sheets said.

I won't engage in utter speculation regarding the nature of the injury, but those comments sound to me like he's about to miss a start.  Or more.