Eric Clapton rose to fame in the Yardbirds

The guitar legend will be joined by BB King, Willie Nelson, Sheryl Crow and Jeff Beck, at the concert - to be held in Chicago on 28 July.

"Some of it's mapped and some of it isn't," said Clapton. "We have to leave a little bit of it to chance."

Pop star Britney Spears recently spent 24 hours at the Crossroads clinic.

Although she quit the facility, she later spent a month at the Promises Malibu Alcohol and Drug Rehab Treatment Facility in California.

It is not known whether she will appear at the concert - which is the second such fundraiser Clapton has organised.

'Life-changing'

A relaxed atmosphere permeated the first Crossroads concert

The first Crossroads Guitar Festival was held in Dallas in 2004. It saw Clapton play classics like Layla and After Midnight with guitarists including Carlos Santana, Joe Walsh, and JJ Cale.

The three-day event also offered guitar workshops, exhibits by leading manufacturers, and displays of guitars from the private collections of Clapton and his friends.

Several of these were later auctioned, with Clapton's treasured Fender Stratocaster - which he called Blackie - fetching a record-breaking $959,500 (�526,000).

All of the events, including this year's concert, will raise funds for Crossroads - which also includes a halfway house and community-education program.

Personal dream

Clapton told the Associated Press that establishing the centre helped him fulfil a personal dream.

"I haven't had a drink or drug for quite a long time and it's changed my life completely. That's something I want to pass on and share with other people."

The 62-year-old guitarist is due to finish his world tour next month, and "have a little break in England" with his family before the Crossroads concert.

"Then I'm going to disappear for a year or two," he said, "and have some fun".