Froome, 30, has already said he had urine thrown at him during stage 14, following media accusations of doping.
The British Team Sky rider said he was unaware of the latest incident but was told about it by journalists.
"We're human beings, and then we're sportsmen. People need to remember that," he said.
"You can't come to a bike race to spit at people or to punch people or to throw urine at them - that's not acceptable at any level."
Froome will carry a lead of two minutes 38 seconds into the final competitive stage on Saturday.
The Kenya-born rider, and Team Sky, have had to defend themselves against accusations of using performance-enhancing drugs throughout this year's competition.
Team Sky released some of Froome's performance data in an effort to end the speculation and prove the rider's innocence.
Team-mate Richie Porte has also said he had been punched during stage 10.
Tour de France leader Chris Froome has hit out at the "appalling behaviour" of some spectators, after he was allegedly spat at during stage 19 on Friday.