An improved protective cap and method for capping medical male luer fittings is provided. The protective cap may include inner and intermediate annular members extending from an end wall and defining a slot therebetween. At least one and preferably a plurality of depressible members project from an outer surface of the inner annular member, wherein the depressible member(s) conforms to the internal threads of a male luer fitting upon interconnection. For such purposes, the depressible member(s) may comprise a resilient material, e.g. most preferably having a modulus of elasticity of between about 5000 psi and 20000 psi. Each depressible member may be of an arcuate configuration in cross-section to present a convex surface for depressible engagement by the collar of a male luer fitting when positioned in the annular slot. The protective cap may be readily employed in automated capping/uncapping procedures via direct linear advancement/retraction relative to a male luer fitting. The protective cap may also be readily rotated onto and off of a male luer fitting. The protective cap and associated methodologies are particularly apt for use in connection with syringes, including automated procedures for pre-filling disposable syringes with medical liquids.