The invention relates to a tip cap assembly (30) adapted to close the fluid passageway (14) of the distally projecting tip (13) of an injection system (10), said tip cap assembly (30) comprising:- an elastomeric inner cap (50) having a frustoconical protrusion (54) extending proximally and having a proximal face (55)；- a rigid outer cap (40) which is or can be securely disposed around said elastomeric inner cap (50)；the proximal face (55) of the elastomeric inner cap (50) having a diameter at least greater than the diameter of the fluid passageway (14) of an injection system (10). The invention further relates to an injection system comprising such a tip cap assembly.
