Fields customarily comes out for postgame interviews, but he did not Saturday.
He also was not among the five players made available for interviews on Tuesday.
“He was able to shake it off, run off the field,” Day said. “We expect him to be fine.”
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Fields carried the ball a career-high 21 times for 68 yards against the Nittany Lions, and his legs figure to be a big part of the game plan again this week assuming he is able to suit up when Ohio State faces nation’s No 4 defense in Ann Arbor.
“When we play in big games like that, we certainly rely on him to run some,” Day said. "It's not typically quarterback design runs, although we have some of those. A lot of them were reading somebody. He can either keep it or run it. Some of those are scrambles when you look at his numbers.
“He does a great job extending plays, but Penn State kind of forced him to run the ball a little bit. He did a great job. Other than the two turnovers, I thought he was unbelievable. We'll continue to do that when we think it's appropriate.”