He later deleted the tweet but today a source confirmed that the reality TV star had checked himself in The Meadows, a trauma and addiction treatment centre in Arizona.
Rob has been rumoured to have been battling weight gain and depression for several months now, and he did not take part in the recent family holiday to Thailand.
A source told America's Star magazine: "Rob has been checked into The Meadows for about a month for substance-abuse issues."
The source added that the 27-year-old has been in the treatment centre for a month, and is feeling better.
His mum Kris Jenner was spotted boarding a plane with Rob at the end of March, and it was then reported that he was heading off to attend a weight loss programme.
The 'Momager' is said to have urged Rob to lose 70lbs ahead of big sister Kim's wedding to Kanye, set to take place in May.
Rob and his mum Kris Jenner
"Rob is well past the point of desperation and now is just flatout miserable," said the source.
"He wants to be the star of the Kardashians for once in his life, but right now he feels like he's bringing the entire family down. He's been feeling stronger and more relaxed without the incessant berating from everyone," said the source.
They continued: "I would love to see him show up a changed man at Kim's wedding and gain some independence."
Rob is also reportedly trying to make amends with sister Khloe’s ex-husband Lamar Odom, who is also battling addiction problems, and to whom Rob was once close, and the source confirmed this, adding: "[He] has completely retreated from the family, and from his friends. But within the last few weeks, Rob has reconnected with Lamar."