A high-pressure fuel pump assembly for use in an internal combustion engine is disclosed. The fuel pump assembly comprises a pumping plunger for pressurizing fuel within a pump chamber during a plunger pumping stroke, and being slidably received in a plunger bore; a rider member co-operable with a drive; and an interface member for imparting drive from the rider member to the pumping plunger to perform the plunger pumping stroke, the interface member having an interface side co-operable with the rider member). The pumping plunger comprises fluid delivery means for delivering fuel from the pump chamber to one or more contact surfaces of the pumping plunger, thereby to lubricate the contact surfaces.