The Dane has struggled to play over 30 matches a season for the Reds since joining the club in 2006 due to a number of serious injuries.
Agger told Danish newspaper BT: "I do not have a long time left. I have considered ending my career for some time.
"I have had some serious injuries, and at times I have considered retiring. But right now I am fine."
The 28-year-old has played in 39 games for Brendan Rodgers's side this season in all competitions.