The invention relates to a needle protector assembly comprising a needle of a disposable medical device and a protective cover for the needle, wherein the needle is attached to a needle hub which can be moved relative to the protective cover between a position of use in which at least the tip of the needle is outside of the protective cover, and a retracted position iii which the needle is fully received in the protective cover, wherein the needle protector assembly further comprises a locking mechanism adapted to secure the needle hub inside the protective cover when the needle hub is in the retracted position.