Ranieri is convinced the work he is putting in on his strike trio will pay dividends, however.
"In the training sessions, I often put the three together to manage better and better in every situation. Then I believe in these three guys," Ranieri told British media.
"There are special sessions, and also when we play matches they stay always together so they can link every time better, to get a better understanding.
"There is a very good link between the three and I think this is a strength of our future."
Slimani has hit the ground running since joining the club for record fee in August with three goals in five appearances but Vardy has not scored since the Algerian's arrived.
"It's important he (Slimani) understands our movement. And his team-mates, understand his movement, he is strong in the air, can hold a ball, it's important the others get around him," Ranieri said.
"He has to improve more how we play and how we move ... he has to understand the Premier League and he can improve more."
Leicester, who are 12th in the table, travel to face seventh-placed Chelsea on Saturday.
(Reporting by Shravanth Vijayakumar in Bengaluru)
