A full-time National Guardsman toting two unloaded M16 assault rifles was allowed onto the Michigan Stadium field before the Michigan-Michigan State football game.
Security officials allowed the man into the stadium, where more than 113,000 people had gathered, because his weapons were empty and no ammunition was found.
A member of the color guard reported the impostor, who was escorted out by police.
Diane Brown, a spokeswoman for the university's department of public safety, told MyFoxDetroit.com that school officials do not believe anything was done "incorrectly or improperly by police in any of the checkpoints."
Brown said the unidentified man cooperated with police, and told officers he used his uniform as a ruse because he wanted to attend the Oct. 9 game but could not get a ticket.
"We escorted him out. He was very compliant and he just continued to explain that he wanted to come to the game, but couldn't get a hold of a ticket and thought he'd use his uniform to be able to do that," she told the website.
Michigan fans told the website they were very surprised about the incident.
"Whether it was good or bad, in a stadium filled with 113,000-plus, I don't think that's the way to handle such a situation," Alex Mandel told the website.
"It's really disappointing because usually the security's really good at the games," Julianne Patterson said.
The man was arrested and released pending a further investigation.
A decision on the charges is expected to come in the next week, MyFoxDetroit.com reports.
The Associated Press contributed to this report.