YOU SAID:

You make me weak in the knees

INTO JAPANESE

あなたは私を膝に弱くします

BACK INTO ENGLISH

You make me weak on my knees

INTO JAPANESE

あなたは私の膝を弱くする

BACK INTO ENGLISH

You weaken my knees

INTO JAPANESE

あなたは私の膝を弱めます

BACK INTO ENGLISH

You weaken my knees