The Italian forked out £7.5million to sign the 19-year-old Poland international from Cracovia in his homeland in the summer, but he has struggled to make any sort of impact at the King Power Stadium so far this season.
Indeed, when Ranieri was asked about Kapustka's chances of forcing his way into the reigning champions' squad, he was unsure.
He said: "Kapustka is a good player and getting better, but I don’t know when he will be ready to play in the Premier League."
Kapustka could end up being loaned out in January in order to gain some valuable playing time experience in England while criticism is mounting over Ranieri's summer spending spree.
Only £29million record buy Islam Slimani has had any sort of impact with the Foxes, as Kapustka and £15million signing Ahmed Musa have barely figured.
In addition, the £13m French midfielder Nampalys Mendy, who was brought in to replace the influential N'Golo Kante, has been out since August with an ankle injury.