The school announced the suspension Monday and included a statement from coach Juwan Howard, who said Michigan takes the matter "very seriously" but did not provide specific details about the violation.
"While we are disappointed with what has transpired with Zavier, we know there are always lessons to learn and grow from," Howard said in the statement. "We take these matters and consequences very seriously. Moving forward, we will continue to handle this matter appropriately within our program and basketball family."
Howard said Simpson's status would be evaluated again after Tuesday's game.
"He knows that the team is going to miss him," Howard said. "He knows he let his teammates down."
The 6-foot-0 Simpson leads Division I in assists (157) and assists per game (8.3) this season. The senior also is Michigan's third-leading scorer, averaging 12.8 points and 4.3 rebounds while playing a team-high 33.8 minutes per game.
Simpson has not missed a game in his Michigan career, a streak of 135 in a row that is now set to end. He is second on the school's career list in assists.
"He just texted us, and he kind of told us he wasn't going to be traveling with us," center Jon Teske said. "That's all I really know."
Michigan has lost four straight and five of its last six, sinking toward the bottom of the Big Ten after a bright start in Howard's first season.
Forward Isaiah Livers is also out Tuesday with a groin injury suffered against Illinois on Saturday. Livers missed six games with a groin injury before returning against the Illini and getting hurt again.
The Associated Press contributed to this report.