After star quarterback Peyton Manning underwent season-ending neck surgery, the Colts collapsed to a league-worst 2-14, missing out on the play-offs for the first time in 10 years.

Caldwell leaves his post with an overall regular season record of 26-22, having enjoyed successful campaigns in 2010 and 2009 with Manning behind centre.

He led Indianapolis to the Super Bowl in his rookie season two years ago, where they were beaten by the New Orleans Saints, but has paid the price for the way his side fell apart with four-time MVP Manning sidelined.

"This was a difficult decision," said Colts owner and chief executive Jim Irsay.

"I think that it was based on the feeling that this was a direction the franchise needed to go, and I wanted to make sure that we took all the time we needed to make sure that it was the right decision."

Caldwell joined the Colts in 2002 as a quarterbacks coach but worked his way up to an assistant coach and eventually took control following the departure of Tony Dungy.

His release comes two weeks after vice chairman Bill Polian and general manager Chris Polian were fired. Ryan Grigson has been appointed as the new general manager.

Doubts remain over 35-year-old Manning's future in Indianapolis, with the franchise now positioned to select Stanford quarterback Andrew Luck with the first overall pick in the NFL Draft.