The Premier League winners are just two points above the bottom three despite spending over £60million in the summer.
After their shock title victory the club broke their transfer record three times by spending £13million on Nampalys Mendy from Nice, £16.6million on CSKA Moscow's Ahmed Musa and then splashing out £30million on deadline day to sign Islam Slimani from Sporting Lisbon.
Mendy has not played since August after suffering an ankle injury while Musa has started just five times in the league and only Slimani, with five goals in 10 games, has made an impact.
Summer signing Ron-Robert Zieler has replaced the injured Kasper Schmeichel in goal on two separate occasions and has kept just one clean sheet, conceding 16 goals in eight games.
Polish winger Bartosz Kapustka, who joined for a fee rising to £5million, is also yet to play but Ranieri dismissed any criticism over their transfer deals.
"The recruitment is very good and I'm very happy but of course it's not always certain when you bring new players that they start very well," he said, ahead of Saturday's trip to Sunderland.
"If you saw Riyad (Mahrez), he started (playing well) in the second year, the first year was normal. If he needed six or seven months then imagine the others. But the recruitment and the system of the recruitment I'm happy with."
Eduardo Macia replaced Steve Walsh as head of recruitment after the former assistant manager left for Everton in July and while the players were targeted long before Walsh left only one new signing - Zieler - started Saturday's 2-2 draw with Middlesbrough.
They are targeting Genk midfielder Wifried Ndidi in the January transfer window, with reports suggesting the Foxes are close to agreeing a deal, while Ranieri conceded the club are keen on adding a defender to aid Robert Huth and Wes Morgan.
"Yes of course, for this reason we are looking in all directions and we need somebody," he said.