The Reds have struggled defensively without Agger, but Benitez could soon welcome him back to the fold.
The Dane played 45 minutes against Manchester United's second string and Benitez was thrilled to see him back on the field.
"It was good for Agger to get some minutes on the pitch and we decided before the game that he would play the first half and Skrtel would play the second," Benitez told The Liverpool Echo.
"Agger did well and now we will have to see how he is today.
"When you have been out for a long time you have to be careful and you cannot rush back because if you come back too early you can have some problems.
"But Agger did well and it was good to see him back playing football again."