"After the announcement of coach Jim Tressel's agreement to join the Colts as a game day consultant, questions were raised with respect to the equity of his appointment as opposed to suspensions being served this season by present and former Ohio State players," Colts vice chairman Bill Polian said in a statement.
"Over the weekend Coach Tressel, Mr. Irsay, Coach Caldwell and I had a discussion of the issue. In addition, we had a conversation with league officials to apprise them of the details of Coach Tressel's employment and the issues we were reviewing.
"At Coach Tressel's suggestion, and with Mr. Irsay's concurrence and support, we have decided to begin Coach Tressel's employment effective with our seventh regular season game. We have informed the league office of our decision and expect that they will be supportive of it. We are very happy Coach Tressel will be joining us."
Tressel, who was brought in to review replays, resigned from his position at Ohio State in May amid an NCAA investigation into rules violations at the school.
Tressel's troubles became known last December when the school announced that five players, including star quarterback Terrelle Pryor, would be suspended for the first five games of the 2011 season for receiving improper benefits in 2009.
Tressel had been Ohio State's head coach since 2001. He guided the Buckeyes to a national championship in 2002. Ohio State won or shared seven Big Ten titles under Tressel.