In a statement to People.com, he says, "For personal reasons, I've checked myself into a rehab clinic. With 2011 being a busy year for Backstreet (Boys), I want to be healthy and at my best. Thank you for all of your support and respecting my family and friends' privacy during this time. I'll see you really soon."

A.J. McLean previously appeared to reference a return to rehab in a post on his Twitter.com blog on 9 January (11), writing, "I love u all and wish me luck! I start my sober journey tomm (tomorrow)!"

The singer has battled addiction for years and enrolled in treatment programmes in both 2001 and 2002 for alcohol and cocaine abuse.

A.J. McLean has been struggling to stay sober in recent months, according to reports, as he faced a gruelling 2011 tour schedule.

Backstreet Boys and New Kids on the Block have announced a joint summer tour, which will begin in Connecticut in June (11).