Credit: Jean Baptiste Lacroix/

Kings of Leon fans were crestfallen on Monday when the band cancelled its entire U.S. tour. Although the band said that lead singer Caleb Followill was "suffering from vocal issues and exhaustion," an insider close to the Grammy winning trio tells Us Weekly the problem is deeper than that.

"They are trying to get Caleb to go to rehab. It is mostly for alcohol," the source says. "[That's why] they ended up canceling the whole tour... he drinks like a fish."

Indeed, the band cut short a Friday concert in Dallas when Caleb told fans "I'm gonna go backstage and I'm gonna vomit, I'm gonna drink a beer," leaving the stage for the night.

Adds a second source: "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."

A rep for the band tells Us: "The reason for the cancellation of the tour is Caleb is under doctor's orders for vocal rest. They feel terrible about canceling. They look forward to getting back on the road at the end of September."

Caleb's bandmate and brother Jared hinted at Caleb's struggles via Twitter.

"There are internal sicknesses & problems that have needed to be addressed," Jared wrote Saturday. "I know you guys aren't stupid. I can't lie. There are problems in our band bigger than not drinking enough Gatorade."

On Monday, after news of the cancelled tour went wide, he added: "Utterly depressed. It's completely out of my hands. Family has to come 1st."

Counters a third band source: "They all drink, all the [bandmates]. Anyone in a band usually likes to have a few beers on the road...They have never discussed [Caleb's drinking] as a problem before."