Wiktionary
a. (alternative form of weak-kneed English)
Usage examples of "weak in the knees".
His smile was potent, a killer smile, and it made her go weak in the knees.
A scent was coming from her, a curious perfume that made him weak in the knees, that turned her words into soft raindrops that fell upon his skin like dew.
He was a sensation, drawing the inviting looks of a number of women weak in the knees at the prospect of winning such a man to their bed.
I stood where I was, weak in the knees but trusting in the protection of Almighty Cyric.
From time to time, though, he would perform some stunt on the blackboard that would leave his professor weak in the knees and the other students baffled and hostile.
He felt weak in the knees, as usual before a fight, but he knew that it would pass.
Those three times had been more than enough to leave him weak in the knees and standing on shaking legs afterward.