Arkley mentioned Butler missed practice with an illness on Wednesday. Perhaps that was why he didn't play.
From Arkley's Messenger article:
Ohio again played short-handed. Sophomore forward Jason Carter was not dressed as Phillips said the preseason All-MAC pick suffered another “setback” with his lower leg injury in practice on Friday. Freshman guard Zach Butler also did not play after missing the last two days of practice with a sinus infection.
Doesn't sound good for Carter. Must be a hell of a sinus infection.