ANN ARBOR -- Changes continue for the Michigan football coaching staff.

And this one might be the biggest domino to fall yet.

Offensive coordinator and offensive line coach Tim Drevno, a long-time confidant and coach alongside Jim Harbaugh, has reportedly resigned from his position at Michigan.

Sports Illustrated's Bruce Feldman and The Wolverine Lounge first reported the news on Friday, three days after Michigan publicly announced the hire of former Florida head coach Jim McElwain.

Former #OhioState and #Minnesota OLine coach Ed Warinner who was hired as an analyst in Ann Arbor is expected to take over the Wolverines OL with Drevno stepping down. https://t.co/GBtpD0D6os — Bruce Feldman (@BruceFeldmanCFB) February 23, 2018

According to Feldman, Ed Warinner, hired by Michigan last month to serve as a senior offensive analyst, will be promoted to coach the offensive line.

A Michigan spokesman said Friday: "I don't have anything to report regarding our coaching staff at this time."

Drevno, 48, spent the last three seasons as offensive coordinator and offensive line coach at Michigan, with varying success.

The Wolverines finished fifth in total offense in the Big Ten in 2015, the first season under Harbaugh, and improved to fourth in 2016. Both years, Michigan posted 10 wins and third-place finishes in the Big Ten East.

But things went backwards in 2017. Aided by early-season red-zone woes, a revolving door at quarterback, a young, inexperienced receiving group, and an offensive line that never seemed to gel, the Wolverines slid to ninth.

Michigan averaged just 348.9 yards per game, a figure that ranked 105th nationally, and allowed 36 sacks on its quarterbacks.

Drevno took the brunt of the frustration from the Michigan fan base as the 8-5 season wore on, even though he was just one of three coaches responsible for the play calling. As of Friday, passing-game coordinator and assistant head coach Pep Hamilton -- also directly involved with game-week preparation, alongside Harbaugh -- remained on staff.

During his signing day news conference earlier this month, Harbaugh said his offensive coaching staff was going through a self-scouting period and job titles were still to be determined.

"We're looking at ways to get our offense up to where our defense is," Harbaugh said.

Less than two weeks later, Harbaugh and Michigan were introducing McElwain, 55, as wide receivers coach. McElwain told ESPN over the weekend that he would also have a hand in coordinating the offense, leaving uncertainty over Drevno's long-term job responsibilities.

Prior to Michigan, Drevno coached alongside Harbaugh at both the NFL and college levels. He was an offensive line coach for the San Francisco 49ers from 2011 to 2013, tight ends and offensive line coach at Stanford from 2007 to 2010, and offensive line coach and offensive coordinator at the University of San Diego from 2003 to 2006.

Drevno was in the second year of a five-year contract that paid him $1 million annually. According to terms of his contract, he may be required to pay Michigan $150,000.

Warinner, well-respected within the college coaching profession, signed a two-year employment agreement with Michigan on Jan. 19 that pays him $250,000 annually in a senior analyst role. His previous stops include Minnesota and Ohio State, where he served as offensive coordinator under Urban Meyer.

Factoring in the Warinner addition, Michigan has its NCAA-maximum 10 on-field assistant coaches on staff.