Which nerve is most likely to be compressed in a painless foot drop?
The common peroneal nerve.
Peroneal nerve palsy usually occurs following compression over the head of the fibula from prolonged leg crossing, squatting, leg casts, and braces. The distal lateral leg often has decreased sensation and decreased foot eversion (superficial peroneal nerve) and dorsiflexion (deep peroneal nerve; foot-drop) are affected because the lesion occurs proximally in the common peroneal nerve.