External support implant for unbound covering of a blood vessel graft in a peripheral vascular bypass system. The implant includes: elongate body having a longitudinal axis, and interior collapsible upon exterior of the blood vessel graft. Elongate body includes tubular fabric having intertwined coiled compression springs configured for elastically resisting longitudinal compression of the elongate body from a relaxed length, when compression springs are slightly stressed, and for elastically increasing diameter of the elongate body when compression springs are subjected to the longitudinal compression.
