Dave Sobolewski was already having a rough season when Northwestern began its Jan. 11 practice.

In preparing for the next day’s game against Illinois, NU coach Chris Collins ran through some of what he called the Illini’s “8,000 pick-and-rolls.”

Sobolewski, Collins said, “got nailed on one of them” and suffered a concussion.

He has not played since. And considering he was not on the bench for Wednesday’s game against Michigan State, the condition might be serious.

A school official said that crowd noise affected Sobolewski on Sunday as he watched the Illinois-Northwestern game from the bench. So NU’s medical staff recommended he stay home Wednesday.

The junior point guard has slumped in Collins’ motion offense, shooting just 25.9 percent and committing a turnover every 11 minutes. Last year the Benet Academy alum coughed it up every 18.3 minutes.