Feinstein said on CNN's "State of the Union" Sunday that the embattled mayor is unable to "provide the kind of leadership that San Diegans want."
Filner's announcement Friday that he will undergo two weeks of full-time therapy defies leaders of his own party who are demanding he step down.
Seven women identified themselves as targets of Filner's unwanted advances that include touching.
Debbie Wasserman Schultz, chairwoman of the Democratic National Committee, urged him to quit and called his alleged behavior "reprehensible."
The San Diego County Democratic Party Central Committee voted 34-6 to ask Filner to resign.
The 70-year-old Filner has acknowledged disrespecting and sometimes intimidating women.