He hit back at comments Gallagher made about the arrival of hip-hop music at Glastonbury Festival being "wrong", describing the rocker's views as "reactionary".
The guitarist suggested yesterday that Jay-Z's addition to the Glastonbury bill was the reason behind the lower number of ticket registrations for this year's event.
Cowan told the BBC: "These are the typical reactionary views of a pampered has-been.
"Having had the grave misfortune of seeing Oasis play Glastonbury in 1995 - a lumpen, turgid mess of a set - Gallagher himself has set the bar very low, and I've no doubt Jay-Z will be a huge success this year."
Festival organiser Emily Eavis also responded to the remarks, pointing out that urban acts including De La Soul, Cyprus Hill and The Roots had all played the summer bash before.
Glastonbury Festival takes place on June 27-79. The full lineup will be announced on May 1.