19-year-old McElderry won the sixth series of The X Factor in 2009, but was dropped from Simon Cowell's label Syco in April and will next appear as a contestant on Popstar to Operastar, which Klass hosts.
Speaking ahead of the ITV show's premiere tomorrow, Klass claimed to understand the 'Ambitions' singer's current state of mind, having had a pop career with Hear'Say and a classical record deal both collapse.
"Even my manager tells me I need to slow down," she told the Daily Mail. "But I'm petrified showbusiness will leave me behind, as it has before.
"I've been where Joe has been. I thought my career was over at 25, but I firmly believe if you work hard enough you'll get there in the end."
McElderry claimed last month that he "expected" to be dropped by Cowell's label, adding: "I could just feel it wasn't right. I kind of knew it. I've had time to digest this and I'm okay with it now."
Popstar to Operastar returns tomorrow at 8pm on ITV1.
Watch the video to Joe McElderry's 'Ambitions' below: