Threet told The Detroit News on Sunday that he has requested and received his release from the school.
"I've decided to transfer from the University of Michigan," Threet told the newspaper in a prepared statement. "I have requested and received my release. I do not yet know where I will continue my collegiate career and will have no further comment until that decision is made."
A redshirt freshman last fall, Threet started eight consecutive games for the Wolverines, leading the team in passing yards (1,105), completions (102) and touchdowns (9). He was expected to compete for the starting job again this spring alongside sophomore Nick Sheridan and true freshman Tate Forcier, who enrolled last month.
Freshman quarterback Denard Robinson will join the competition this summer.
Threet already has transferred once, from Georgia Tech to Michigan before the 2007 season. He sat out 2007 and competed with Sheridan for the starting job last season.
Michigan opens spring practice March 14.
Adam Rittenberg covers the Big Ten for ESPN.com. He can be reached at firstname.lastname@example.org