NICK Duigan has officially retired after Carlton received AFL permission to place the defender on its long-term injury list next season.
The Blues confirmed Duigan's retirement on Monday and will now be able to elevate a rookie to replace him on its senior list next season.
Carlton football manager Andrew McKay refuted reports the Blues had been "blindsided" by Duigan's decision, which was made too late for Carlton to replace him at the NAB AFL Draft or the Pre-Season Draft, or with a free agent.
"This is not a situation that has taken us by surprise," McKay said.
"Nick has had an ongoing knee condition which both he and the club were hoping could be managed through 2014.
"Unfortunately, the doctors have now made it very clear that his knee will not cope with another year at AFL level.
"To suggest that Nick has somehow let the club down by not reaching his decision earlier is simply inaccurate.
"At all times Nick has been entirely open and honest about the condition of his knee, and his ability to play on."
Duigan, 29, started pre-season training with Carlton's first to fourth-year players last month, but said he soon realised his knee problems would not allow him to play on.
"It's been a difficult decision, but it's certainly the right one for both myself and the club," Duigan said.
"I want to thank Carlton for giving me the opportunity, it has been a fantastic club to be a part of."
Duigan played 43 games in three seasons with the Blues after being a surprise mature-age selection in the 2010 NAB AFL Draft at pick 70.
At the time, Duigan had just completed a Masters degree in psychology and intended to work in Sudan for a year with his girlfriend as a volunteer.
He was named Carlton's best first-year player in 2011, and won the club's Player Ambassador Award this year.
McKay said Duigan had been a terrific leader at Carlton.
"Nick has been really hands-on with work in the community and has acted as a mentor for both our players and youth in the Carlton area," McKay said.
"We would like to thank him for his contribution and wish him well in the future."