A support assembly for a deformable sealing element of a downhole tool such as a packer, bridge plug or straddle. The support assembly has first and second support devices at each end of the sealing element with each device having an elastically deformable support member adapted to be located between the respective end of the sealing element and an actuating member of the downhole tool. Additionally, a guide member with an inclined guide surface is provided such that the support member travels along the inclined surface when a force is exerted by the actuating member to expand the sealing element radially into abutment with a surface downhole. The support member moves radially outwards to support the respective end of the sealing element during deformation.