Steven Tyler's Aerosmith bandmates are increasingly worried about the singer's state of mind as he embarks on a two-year hiatus he refused to tell them about.

The rocker left his longtime bandmates stunned when he revealed his plans to take a lengthy break from the group in a magazine interview last month, prompting Joe Perry, Joey Kramer and Brad Whitford to seek out a new singer for their 2010 recording and touring plans.

And, after a month of bickering, Tyler's bandmates now admit they're worried about their frontman's health and well being.

Drummer Kramer tells Billboard.com, "Steven, he isolates more and more all the time - that's what gives it away to me that there's something going on.

"I don't know what that is. I know he's made some not so great choices and he's got some negative influences around him now. I love the guy. I just want to see him get some help."

Kramer's comments come at the end of a difficult year for Aerosmith - Tyler upset his bandmates when he split from the group's management company and then the band was forced to scrap a summer tour when the singer fell from the stage and shattered his collarbone during an August concert in South Dakota.

Tyler has also been forced to deny reports linking him to substance and alcohol abuse, but his bandmates aren't convinced he's clean.

Whitford adds, "This guy has a tremendous history of drug abuse, and you have to be suspicious that this is something that's probably going on with him. I have a feeling we might be looking at someone who's just really struggling very badly."

And Whitford tells Billboard.com that Tyler's behaviour in recent years has become "more erratic and unreasonable".

Kramer admits the rocker has ceased communicating with his bandmates: "I have called him and left voicemails and texted him to no avail... I get no reply. One of his biggest things is that, 'Well, nobody calls me.' Well, that's bulls**t, 'cause I have. I've always been there for him and I probably always will be. I can only hope and pray that Steven will put the focus on Steven and get healthy."