The Dane suffered the blow during the Foxes' goalless draw with Copenhagen, but only realised the extent of the damage when he went to bed after the clash.
Ron-Robert Zieler will be between the sticks for Sunday's Premier League match against West Bromwich Albion at the King Power Stadium, and Ranieri is "confident" in the second-choice keeper's ability.
"The hands for keepers, like the hands for boxers, are very, very important," Ranieri told reporters in Friday's press conference. "I don't put a deadline because every man is different. Maybe two weeks, maybe three. Maybe five, six, seven - I don't know. Kasper wants to play Sunday. It's normal.
"Only in the night he felt something. It's unbelievable. Maybe [it was because of] the adrenaline, the concentration, that he didn't feel anything [during the match].
"I'm very confident with Zieler. Of course Kasper was in great condition but Zieler gives me confidence."
Schmeichel underwent surgery on Thursday.