The Spain international striker has scored six goals in eight games since his former Liverpool boss Benitez took over from Roberto Di Matteo and the gaffer is thrilled with how things are going up front for the Blues.
"Fernando worked and is working very hard. He can still improve and he knows it," Benitez told Spanish radio station Onda Cero.
"We are making small changes to the team and the motivation.
"His principle objective has to be attacking, and to be as close to the area as possible."