Scott was then tested for the virus, and after being given the all clear, he was allowed to join the other patients in the facility on Friday.
A source said: "Scott flew in on Tuesday and had to Zoom in to a group meeting from his room to introduce himself.
"He said he's having trauma from his past, he mentioned trouble with his ex and said he's also having trouble with his children and he's been taking cocaine and drinking a lot.
"He looked pretty skinny and told the group he was coming to rehab to work on his issues and said he was having withdrawal symptoms and was tired and lethargic.
"He told staff he didn't want any special treatment during his stay, in terms of meals and therapy."
Scott has been honest about his personal struggles in the past, and said on a recent episode of E! reality show Keeping Up with the Kardashians that he was finding it difficult to come to terms with the death of his parents, especially now that his children - Mason, 10, Penelope, seven, and Reign, 5, whom he has with ex-partner Kourtney Kardashian - are beginning to ask about their grandparents.
The star's mother Bonnie passed away in 2013 after a long illness, while his father Jeff died of unknown causes in 2014, and Scott - who is now romancing Sofia Richie - was extremely close to both of them.
He said on the show: "Losing my parents is not an easy subject for me to talk about. It puts me in a very vulnerable place, to remember them and think about them."