The invention relates to a tip cap assembly (40) adapted to close a fluid passageway (27) extending through a tip (23) of a container (20) of a medical injection system (10), the tip cap assembly (40) including: a rigid outer cap (41) including an inner skirt (44) extending proximally and having an outer threaded surface (44a), an elastomeric inner cap (42) arranged within the outer cap (41), the inner cap (42) having a protrusion (42a) extending proximally and adapted to close the fluid passageway (27), characterized in that the outer cap (41) further includes an outer skirt (45) extending proximally and around the inner skirt (44) so as to define an annular groove (46) between the inner skirt (44) and the outer skirt (45), and that the outer skirt (45) includes a proximal member (48) having a projection extending inwardly or a recess depressed outwardly.
