Jose Callejon scored a wonder goal to draw the home side level in the Coppa Italia last-16 clash following Giuseppe De Luca's opener, before Lorenzo Insigne and a second Callejon strike sealed the win for the Partenopei.
Wednesday's two-goal hero was one of Benitez's summer acquisitions and he is adamant that another new face will be brought to the San Paolo this month.
"I'm sure the president will do something this week," Benitez told reporters. "One hundred percent. He said that's what he'll do and I expect him to. I will not speak about who, though. I do not want to speak about players who are not yet at Napoli.
"It's not easy to find players in January, so it is difficult to complete deals. However, I am confident that the president will make one or two coups this week."
Napoli faces Lazio in the Coppa Italia quarterfinal stage, with a semifinal against Roma or Juventus on the cards, and Benitez is pleased that his side did not let going a goal behind deter it from victory.
"We knew this could be tough, as Atalanta work very hard, but we reacted well to the opening goal."