Bill O’Brien is leaving Ohio State only three weeks after he was hired as the Buckeyes’ offensive coordinator and quarterbacks coach.

He was announced Friday as the next coach at Boston College, replacing Jeff Hafley who left to become the Green Bay Packers’ defensive coordinator last week.

O’Brien, a 54-year-old native of Massachusetts who was the offensive coordinator with the New England Patriots last year, had been widely perceived as the front-runner in recent days.

Along with his ties to the Northeast, he has previous head coaching experience with the Houston Texans from 2014-20 and Penn State from 2012-13, leading the Nittany Lions in the aftermath of the Jerry Sandusky child sexual abuse scandal.

The departure leaves a sizable hole on Ryan Day's coaching staff at Ohio State as he had intended to turn over play-calling responsibilities to O’Brien, a significant shift in his role leading the Buckeyes.

Day has largely called the offense since he arrived as an assistant in 2017 and continued after he was promoted to replace Urban Meyer.

But it might not take Day long to fill the vacancy as reports mentioned Chip Kelly as the likely replacement after he resigned as UCLA's coach later Friday. The Los Angeles Times reported that Kelly had accepted the position.

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Day has known Kelly for more than two decades, dating back to when he was a quarterback at New Hampshire from 1998-2001 and Kelly was the Wildcats' offensive coordinator.

Kelly also hired him as his quarterbacks coach with the Philadelphia Eagles in 2015 and San Francisco 49ers in 2016.

Another assistant coaching vacancy had already remained after Day fired special teams coordinator Parker Fleming last month.

He said this week that he is looking at an assistant for the defense or special teams in a search that could last another week.

Joey Kaufman covers Ohio State football for The Columbus Dispatch and can be reached at jkaufman@dispatch.com.

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This article originally appeared on The Columbus Dispatch: Bill O'Brien leaves Ohio State for Boston College head coaching job