Everton have won just once in their last 11 matches, with the pressure building on Ronald Koeman.
The Toffees were booed off the pitch, following their latest defeat against Watford at the weekend.
And Redknapp believes that Everton’s squad needs an injection of quality in the January transfer window.
“They need one or two new players,” Redknapp said. “He’s taken over an ageing team. Three or four years ago, they were good players. But they are not getting any younger.
“Lukaku, you are never sure what you are going to get with him. They need to strengthen their squad in the window, if they can. One or two of them have had their better days.”
Everton started the campaign in fine form, but their form has dipped badly in recent weeks.
The Toffees are now in ninth place in the Premier League table - and there are concerns about which direction their season is heading in.
Everton are expected to have funds to spend in the January transfer window, with Farhad Moshiri prepared to back Koeman.
The Toffees are next in action on Tuesday evening, when they take on Arsenal at Goodison Park.