A hint by Glastonbury Festival founder Michael Eavis that the headline act will be a top band has sparked a frenzy of speculation.
Mr Eavis, who launched the world famous festival on his farm in 1971, told the Bristol Post on Tuesday the headline act would be "one of the biggest-selling bands in the world at the moment".
He also said the band would be making their first appearance at Worthy Farm.
His comments sent the rumour mill into overdrive on fan sites and social media over who it could be, with Metallica the clear favourite.
The band played live at the Apollo TheatreHoly Moly said a source had told them Metallica was the band.
Gigwise also said it was most likely to be the rock band, but added it could also be Daft Punk.
The announcement ruled out Oasis, who had earlier been identified as the headliner for Saturday on the main Pyramid Stage.
They have also appeared several times at the Grammy AwardsIt also ruled out solo acts Prince and David Bowie, and Fleetwood Mac, who do not have huge current sales.
Whoever it is will join the already confirmed Arcade Fire and Kasabian who will take the top slots on Friday and Sunday.
Fans reacted with enthusiasm to the possibility one of the biggest and loudest bands in the world would play the world's top music festival.
The band has sold more than 50 million albums, according to SoundscanJpee, on the glastowatch forum, said: "Metallica deffo deserve the spot if they get it. They are a huge band and the back catalog is stupendous."
Jonny deep added: "I'd love to see Metallica."
There was one possibility that could leave thousands of Metallica fans with tickets devastated, however, as a large number of posters were also speculating the band might be One Direction.