The veteran NFL running back is not a fan of the Michigan head coach.
The Brandon Jacobs-Jim Harbaugh feud has escalated.
Jacobs, a nine-year NFL running back who last played in the league in 2013, spent one year under Harbaugh in San Francisco in 2012.
Apparently, that year didn't go very well.
Jacobs told CBS Sports Radio's 'Tiki and Tierney Show' earlier this week that Harbaugh had "no idea" what he was doing.
"I knew more about football than they led on," Jacobs said. "Going somewhere where they didn't have route conversions into certain coverages was just absurd. They were just running routes in the defense and getting people killed."
Harbaugh responded on Twitter.
Jacobs wasn't done.
Jacobs went as far to say he'll get Harbaugh fired by Michigan when he's done exposing him.
"Love the support but stop the super bowl talk. I will expose him, Michigan will fire him when I am done," he wrote.
Bigger rival for Jim Harbaugh: Brandon Jacobs or Urban Meyer?