The Spanish side is considering making a move for the Danish defender in the January transfer window.
Sanchez told Danish web site kunsport.dk: “We already had plans to buy Agger this summer, along with a lot of other players.
“But the Robinho affair gut too much attention, and we used a lot of resources on it, so we were forced to drop our move for Agger and other players we wanted.”
Agger has refused to commit to a new deal at Liverpool until manager Rafa Benitez confirms whether he has a first-team future at the club.
Sanchez continued: “He is a player we have watched for a long time and we will probably make a bid for him in January.
“He is a world class player and he will without doubt fit or system. What we need at the moment is a defender and an forward, and at the moment Agger is at the top of our list of targets.
“But I must also say that we have not decided on who we will make a move for yet and we are still working on our transfer-strategy for January.”
Agger joined Liverpool in 2006 from Danish side Brondby.