Lucas Harrell is apparently available out of the bullpen today and has apparently been bumped from the rotation, according to Brian Smith. Even more strange and possibly indicative of the reasoning behind it, Harrell seems pissed, telling Smith, "I don't want to talk about it."
Harrell pitched - ineffectively - on Friday, meaning his next scheduled start would be at St. Louis on Wednesday. Then his next start would be on the first day of the All Star Break. So it's possible they're just skipping his turn in the rotation, and will make some sort of starter decision later. Oberholtzer, possibly, because I refuse to get my hopes up about Jarred Cosart - and I don't think they would make his Major-League debut at St. Louis, and there would be other transactions to make before it could happen.
Update: Harrell has indeed been sent to the bullpen.