The Washtenaw County, Mich., prosecutor's office said last month Gibbons -- who was expelled in 2013 for violating a sexual misconduct policy -- does not face criminal charges for allegedly raping another student at a frat party in 2009 when he was a redshirt freshman.
Gibbons was in graduate school and had nearly completed his football eligibility when he was expelled prior to the Buffalo Wild Wings Bowl game Dec. 28.
He did not attend that game, Coach Brady Hoke announcing at the time Gibbons had returned home to Florida for "a family matter."
The Detroit Free Press reported Wednesday the U.S. Department of Education is investigating the matter, citing a letter from the Office of Civil Rights.
The letter said the division will look into whether university officials handled the matter appropriately, and whether students on the Michigan campus are safe from sexual assaults, the newspaper reported.