The French midfielder, who was injured while making his Premier League debut for the club against Arsenal in August, has missed the Foxes' last nine matches.
Ranieri, speaking at his pre-match press conference ahead of the Champions League visit of FC Copenhagen on Tuesday, revealed the ex-Monaco man had gone under the knife.
"Today he's under surgery to clean little fragment of the bone," said the Italian.
Mendy should be back to bolster Ranieri's options in time for the busy Christmas and New Year programme of fixtures and he could even be available for the final Champions League group game away at Porto.
The manager also confirmed that Shinji Okazaki, who picked up a knock while on international duty with Japan, is fit to face Copenhagen after missing the defeat to Chelsea on Saturday.