Grevillea microstegia (Mount Cassell grevillea) is a spreading shrub which is endemic to the Grampians National Park in Victoria, Australia. It grows to between 0.3 and 1 metre in height and 2 to 4 metres in width. The flowers are reddish-brown and have green-tipped red styles. These appear between November and December (late spring to early summer) in its native range. The species was first formally described by Bill Molyneux in Muelleria in 1975. Grevillea microstegia is endemic to the Mount Cassel area in the Mount William Range, north-west of Moyston, Victoria.