In December (15), the trio announced they were going on tour, and the European leg of the trek kicks off in France on 26 June (16), the day Britain's iconic music festival ends.
Their tour includes a stop at the Heineken Music Hall in Amsterdam, Netherlands, and a notice on the venue's website has apparently given away the ZZ Top Glastonbury appearance.
It read, "ZZ Top comes in June and July 2016 for 20 concerts, which are all part of their new roadshow to Europe. The Hell Raisers Tour kicks off in Birmingham to travel further then (sic) to the renowned Glastonbury Festival in Pilton."
The message has since been removed from the website, fuelling speculation the announcement was correct.
The band and Glastonbury organisers have not commented on the rumour.
No acts have been confirmed yet, but Coldplay, Muse, and Adele are all hotly tipped favourites for the headlining slots. Foo Fighters are also rumoured to be performing at the festival after pulling out last year (15) due to Dave Grohl's leg injury.
Glastonbury, the largest rock festival in the world, runs from 24 to 26 June (16).