Ranieri was forced to defend his club's transfer business as questions intensify about the impact of their signings.
Ranieri backed his title-winning stars after criticism of their league form, which has fallen well below last season's remarkable standards.
The Italian, whose team are only two points above the relegation zone, attempted to explain the difference between his side's stellar Champions League performance in their debut season and their poor displays in domestic games.
Ranieri was also forced to defend his club's transfer business as questions intensify about the impact of their signings.
Club record buy Islam Slimani, who is in line to start at the Stadium of Light, is the only one of the new recruits to make a significant impact with five goals in 10 games since the forward's arrival from Sporting Lisbon.
But Ranieri said: "The recruitment is very good and I'm very happy, but it's not always certain when you bring in new players they start very well.
"Riyad Mahrez started (playing well) in his second year. If he need six or seven months, imagine the others."
Ahmed Musa, a striker signed from CSKA Moscow, has started just five league games so far, while winger Bartosz Kapustka has not played at all.
Free transfer defender Luis Hernandez has made just three league appearances and goalkeeper Ron-Robert Zieler has been unconvincing.
Midfielder Nampalys Mendy, who was signed from Nice to replace the influential N'Golo Kante after his move to Chelsea, has made just one appearance due to injury.
But Mendy, 24, could return to the squad at Sunderland after training this week following ankle surgery.
"He has worked with us and done all the training sessions this week pain-free," Ranieri said.
"He lacks stamina but he is getting better. I have to decide but think he is OK for the bench. Maybe he can play for half an hour."
Meanwhile, Adnan Januzaj insists Leicester hold no fears for struggling Sunderland.
David Moyes' side are looking to bounce back from the 2-0 defeat to Liverpool that saw them drop to the foot of the league table.
Januzaj is confident Sunderland can produce a repeat of their most recent outing at the Stadium of Light, when they beat Hull 3-0 to boost their hopes of pulling off a fifth consecutive successful relegation fight.
Victory would leave the Wearsiders just two points behind Ranieri's side at the bottom.
Januzaj hopes to make his first start for more than two months after recovering from an ankle problem, and he said: "Leicester won the league last year, but we're at home, and it's a game we should be aiming to win.
"Just because they were successful last year doesn't mean we have to put ourselves down.
"We will head into the weekend confident and hopefully we can take three points."
Injury and suspension has restricted Januzaj to just six starts, with one goal, since arriving from Old Trafford in mid-August.
The Belgium international hopes to make up for lost time by forcing his way back into the side, and he added: "The injury came at a bad time, because I was getting into my rhythm, but I'm getting back now and I'll be on top of my game very soon.
"There are lots of matches over Christmas and every player is needed, so we will all get a lot of playing time because we have some big games coming up."