Chink in one's armor

The idiom "chink in one's armor" refers to an area of vulnerability. It has traditionally been used to refer to a weak spot in a figurative suit of armor. The standard meaning is similar to that of Achilles' heel.

Grammarist provides a sample usage by The Daily Telegraph that they find acceptable: "Such hype was anathema for the modest professional fighter, who has 22 victories under his belt, and not a perceptible chink in his armour."