Kings Of Leon's cancelled US tour could cost up to $15 million.

The band pulled out of 29 scheduled dates in North America earlier this week citing exhaustion and voice problems on the part of lead singer Caleb Followill, which could lead to their insurers, Lloyds of London, landing a bill running into tens of millions as promoters and concert venues claim for lost revenues.

Industry figure Dennis Arfa - who is an agent for Metallica, Billy Joel and Rod Stewart - claims "exhaustion," is not likely giving the full picture.

He told "Well, I mean, it tells me stuff is going on. Something's not right, obviously.

"Exhaustion is a label. It doesn't tell you the detail - just says 'exhaustion.' Exhaustion usually means you have issues going on beyond just being physically tired. It's a convenient label."

Problems in the band appeared to surface after Caleb cut the band's set short in Dallas, Texas, last Friday (29.07.11) complaining of the heat and his voice.

The band's bassist, Jared Followill, later tweeted: "There are internal sicknesses and problems that have needed to be addressed.

"I can't lie, there are problems in our band bigger than not drinking enough Gatorade."

It has also been rumoured the rest of the group - Caleb's brothers Jared and Nathan, and their cousin Matthew Followill - have urged the singer to go to rehab.

A source told "They are trying to get Caleb to go to rehab. It is mostly for alcohol."

A second source added: "It's true. Caleb's drinking is out of control and they are trying to get him into rehab. It's a dark demon he has been fighting for awhile."