Rob, 28, has withdrawn from the spotlight recently and 30-year-old Khloe revealed he is struggling with anxiety.
She told WonderWall: “I just feel, especially over the last year, Rob has become very introverted and has a kind of social anxiety.
“He’s definitely not at his happiest place that he once was, and I know he can get to that happy place and he will.”
Rob’s anxiety got so bad last year that he skipped sister Kim’s wedding to rapper Kanye West.
But Khloe has insisted she knows her brother will work his issues out. She continued: “We all kind of get to a place where you don’t know where to go in life or whatever, so I think it’s important for him to know that he always has people to lean on and it’s not unnatural for people to not know where to begging. It’s a growing process. I will always be his number one supporter.”
Rob’s problems allegedly started when he gained weight and he has since spoken out about trying to get back into shape.
Hitting back at online trolls earlier this year, Rob wrote: “Last throwback of the day and yes I’m fat now so yall haters can literally suck d*** [sic]”