Former Ohio State offensive coordinator and line caoch Ed Warinner, brought in an offensive analyst, would be the obvious choice to replace Drevno as line coach.
Michigan's offense was horrendous in 2017 and many fans and analysts have pointed the finger directly at Tim Drevno for his playcalling.
Drevno, 48, spent the last three seasons as offensive coordinator and offensive line coach at MI, with varying success.
Coming off a five-loss season and a down recruiting year, Harbaugh has made major changes to his staff ahead of his pivotal fourth season at MI.
There is no question about it, the heat is certainly on for Harbaugh, who has yet to prove he can beat his biggest rivals or win a Big Ten Title. The Wolverines averaged 348.9 yards per game and an offensive line that has lacked consistency the last several years, gave up 36 sacks.
"We're looking at ways to get our offense up to where our defense is", Harbaugh said.
Drevno's resignation has come after MI head coach Jim Harbaugh announced the hiring of Jim McElwain to be the wide receivers coach on February 20th.
ESPN.com's Chris Low reported McElwain will be involved in developing weekly game plans and coordinating the offense.
Prior to Michigan, Drevno coached alongside Harbaugh at both the National Football League and college levels. They coached together at San Diego, Stanford, with the San Francisco 49ers and at MI.