No. 8 Michigan opens its season against the second-ranked Crimson Tide Saturday in Arlington, Texas.
Both Toussaint and Clark had legal problems this summer but Michigan Coach Brady Hoke said he didn't make a decision on the suspension until Friday.
"The decision was not easy but I feel it is in the best interest of this program and for these kids and those always will be my priorities," Hoke said in a statement. "We have choices every day and you have to be accountable to this program, your teammates, your family and the University of Michigan."
Toussaint pleaded guilty this week to a misdemeanor charge of driving while impaired. Clark has been charged in a home invasion case.
Toussaint, a junior, last season rushed for 1,041 yards and nine touchdowns, both second-most for the Wolverines. Clark, a sophomore, had 10 tackles last season.