MI will be without its leading pass catcher for the foreseeable future.
Harbaugh said the team does not have a timeline for Black's return, but it's possible that he could miss the entire season.
The 6-foot-3, 206-pound receiver from CT had amassed a season-high 11 catches for 149 yards and a touchdown in the first three games for 8th-ranked MI (3-0), which opens Big Ten play on Saturday at Purdue (4 p.m., FOX). Black hurt his left foot Saturday against Air Force.
"He's going to be out and going to need surgery", Harbaugh said.
"He's going to be out", Harbaugh told reporters during his weekly news conference. "He's got a crack in his foot, on the outside of his foot".
"I don't know", the coach said. Black would be eligible for a medical redshirt year since he has played only three games thus far.
MI running back Ty Isaac also was injured on Saturday, but Harbaugh said that was nothing serious.
"Next man up we preach", receiver Eddie McDoom said.
"Next man up, just take his place and make those big plays", he continued.