The Argentine is out for the season after scans showed he suffered serious ligament damage to the knee in the clash with Brescia.
That has left Benitez short of defensive options and he has been given the green light to bring in reinforcements in the transfer window.
Danish international Agger is top of his wish list. The pair worked together during Benitez's time at Anfield, says the Mirror.
And it was on the insistence of Benitez that the Anfield board agreed to hand the defender a new four year, £70,000 a week deal in May 2009.
Agger has missed a large chunk of the season with a calf problem but Benitez is hopeful he will recover his fitness by the time the transfer window opens.
And Benitez said: "Since we've lost such an important player as Samuel, we will have to arrange the roster in January.''