Bono's injured back forces U2 to pull out of Glastonbury

(PA)

It's the kind of news any festival director dreads. With just four weeks to go, Glastonbury's Friday-night headliners U2 have pulled out.

After injuring himself while training for their tour last week, singer Bono underwent emergency surgery on his back on Friday in a measure to prevent possible paralysis and doctors advised the 50-year-old to recover for two months.

Glastonbury has had its fair share of trials in recent years from torrential rainfall to the initial doubt over Jay-Z's appearance in 2008, but U2's cancellation could be the biggest turbulence to hit the festival in a while.

Of course the question that everyone, especially the 177,000 ticket-holders, is asking is who will the organisers, Michael Eavis and his daughter Emily, find to fill the void left by U2, widely regarded as the biggest band in the world?

The problem is that Glastonbury has set its standards high; U2's 30 years of performance and influential albums will be hard to match. Among the many acts being muted as possible replacements, Coldplay are high on the list. With just four weeks' notice, booking Coldplay could be one of the easier options; the band are personal friends with the Eavis family and headlined in 2002 and 2005. But for a festival that has worked hard to shake up its image of being too middle-aged and respectable, such a safe decision could be seen as a step backwards.

Arguably, Glastonbury has the modern rock act covered with Muse – one of the world's best live contemporary rock acts – headlining on the Saturday. Many would prefer to see an enduring veteran rock act such as Paul McCartney or David Bowie, while Led Zeppelin's Jimmy Page told BBC 6 Music that he would not rule out an appearance, although with Neil Young and Bruce Springsteen headlining last year, the festival could find itself accused of not being youthful enough.

Among the newer rock acts, Arcade Fire are ruled out by their exclusivity to the Reading and Leeds festivals. Radiohead, meanwhile, would be an instant hit. Having established themselves as one of the most groundbreaking acts over the past 20 years, they certainly have the back catalogue, but the Oxford band refused to play in 2008 because of Glastonbury's poor transport links, which go against their environmental credentials.

The greatest coup of all would be bagging the Rolling Stones, who have yet to play the festival. Currently at No 1 in the UK album charts for their re-mastered Exile On Main Street, they are very relevant today and Michael Eavis has been trying to book the rock legends for years.

But surely the fact that Glastonbury tickets sold out last October – months before the line-up was even announced – suggests that those who bought tickets aren't too bothered about who is headlining.