Fibularhizoctonia is a genus of fungus in the Atheliaceae family.

The genus, circumscribed in 1996,[1] contains three widespread species that are anamorphs of Athelia.

[2] One species of Fibularhizoctonia is commonly known as the cuckoo fungus[3] because it makes sclerotia, also called termite balls, which mimic termite eggs.

[5] The generic name had been incorrectly modified to "Fibulorhizoctonia"[2] in some publications but this change is not a nomenclaturally supportable spelling correction.

The genome sequences of two species of Fibularhizoctonia have been described.