Harbaugh was uncertain whether Black, who missed most of last season with a foot injury, would need surgery.
The fracture is similar to the one Black suffered last year to his left foot, according to Harbaugh.
Black, who was hurt during practice Saturday, had 11 receptions for 149 yards and a touchdown in three games last season before his season-ending surgery.
The 14th-ranked Wolverines open the season Saturday night at No. 12 Notre Dame.
ESPN's Adam Rittenberg and The Associated Press contributed to this report.