A Euphonium Extension Rest for a portable device to support a musical instrument such as a baritone horn, a euphonium, a small tuba, or a similar instrument with a portable stand so that a musician can handle the instrument for lengthy sessions; the device includes an extendable wrap with a left-hand and right-hand curved side rail and a bottom half of a hemisphere, a protection cushion contiguous to the curved side rails, a way to secure the protection cushion to each of the left-hand and right-hand curved side rails, and a securing manner to releasably encircle the musical instrument to hold the extendable wrap.