"Even after his medical scare, Rob acts like he wants nothing to do with the world," the source said. "He doesn't respond to texts from people that are genuinely concerned and checking up on him."
Days after Christmas, the reality star was rushed to the hospital for stomach problems, with some reports citing his diagnosis as diabetes. Over the past two years, Kardashian, 28, has lived a life of seclusion, staying out of the public eye as he battled depression and gained over 100 lbs.
Exclusive: 'I Can’t Win Life for Him' Says Khloé about Her Reclusive Brother Rob Kardashian (VIDEO)
Family matriarch Kris Jenner put her St. Barth's vacation on hold when she learned the news, flying back to Los Angeles to support Kardashian after his hospitalization.
Jenner, 60, returned to the island on Thursday to resume her vacation with boyfriend, Corey Gamble.
Even with the alarming diagnosis, Kardashian has remained out of touch. The source adds that he's back living with his older sister, Khloé Kardashian and has been unreachable.
Although Kardashian is continuing to be reclusive, the source says once the holidays come to a close, the family will figure out how to handle the situation.
"The family will come up with a new plan when the holiday is over and everyone is back in L.A.," the source told PEOPLE. "They are of course very concerned about Rob and have been for a long time."