A passively shieldable needle assembly set is provided for use with a tube holder. The assembly includes a needle cannula, a hub mounted to the needle cannula and a tip guard slidably movable along the needle cannula. The tip guard can be slid into a distal position where the tip of the needle cannula is safely shielded. A collapsible guard drive is mounted to the hub and includes a pair of collapsible leaves extending from the hub to the tip guard. The leaves have a length that enable the tip guard to move into shielding engagement around the tip of the needle cannula, while preventing complete removal of the tip guard from the needle cannula. The leaves are resiliently deformable and can be collapsed onto themselves and onto the hub. The leaves can be retained in their collapsed condition by a packaging cover and subsequently by the grip of a medical practitioner. A mere release of the grip on the collapsed leaves enables the leaves to resiliently return toward an undeflected condition and propels the tip guard distally into shielding engagement around the tip of the needle cannula.