Last week, it was reported that McLean has sought treatment at a rehabilitation clinic due to an undisclosed personal struggle.
In an interview with North Carolina's Bob 93.3 FM radio station, Littrell explained that he views McLean's decision to seek professional help as a positive step.
"I'm proud that he would go into this situation willingly," he said.
McLean previously spent time in rehab in 2001 after battling depression, anxiety and alcohol dependence.
"Last time it was a lot worse. He really went into rehab unwillingly the last time," Littrell added.
Backstreet Boys are scheduled to embark on a tour with fellow boyband New Kids On The Block later this year.
[digitalspy.co.uk]
