Rumours that the US heavy metal group will perform on the Pyramid Stage in June have been rife in recent months, particularly after drummer Lars Ulrich described the gig as "the one festival to elude us" last October.
"Every year there's probably less chance of us doing it than the previous year, but it just looks like it would be a fun night out," he told MTV.
"There's such a vibe and it’s maybe the most quintessentially English festival. Everybody who goes there loves it. We're in the Yellow Pages and ready to go!"
Glastonbury organiser Michael Eavis has raised doubt over the inclusion of similar bands in his line-ups, arguing in 2002 that “you get crowd-surfing and all those things that seem to cause problems”.
Along with Metallica, Prince is Paddy Power’s 5/4 favourite, despite co-organiser Emily Eavis saying that booking the “Purple Rain” singer “wasn’t happening this year”.
Kasabian are also a popular choice at 5/1 to headline on Saturday, with Fleetwood Mac at 9/1 and Elbow at 10/1.
Tickets for Glastonbury (25-29 June) sold out in record time, with 120,000 booked in just one hour and 27 minutes. More than one million people have registered for 2015 tickets.