Travis Barker was reportedly hospitalised for pancreatitis triggered by a colonoscopy.
The Blink-182 drummer, 46, is still in medical care at Cedars-Sinai Medical Center, Los Angeles, California, with his new wife Kourtney Kardashian, 43, at his side.
TMZ has reported Barker's doctors believe his pancreatitis was "triggered" by a recent colonoscopy, with sources telling the site the musician recently underwent the invasive examination.
The site says "multiple sources connected to the family" confirmed the cause of his medical emergency.
A source also told Entertainment Tonight: "Travis was sick and had intense pain in his abdomen and it really concerned him and Kourtney.
They called 911 and he was rushed to the hospital. After speaking with Travis and running several tests, doctors said Travis is suffering from pancreatitis."
Colonoscopies are usually performed to look for changes in the large intestine such as swollen, irritated tissues, polyps or cancer. In extremely rare cases the routine exam can cause inflammation of the pancreas, which usually requires hospital treatment and can last anything from days to years, with symptoms including upper abdominal pain, nausea and vomiting.
It comes after Barker was raced to West Hills hospital earlier this week before being transferred to Cedars Sinai.
He was pictured being wheeled into the facility after tweeting: "God save me" at around 10.45am local time on Tuesday.
Barker's daughter Alabama took to her Instagram Stories to ask the drummer's fans to "Please send your prayers" alongside a sad emoji.
She also posted a now-deleted image of herself holding her father's hand as he lay in a hospital bed, captioning the photo, shared on TikTok: "Please say a prayer."
It comes weeks after Barker and mum-of-three Kardashian – who has children Mason 12, Penelope, 9, and 7-year-old Reign with her 39-year-old ex-partner Scott Disick – got married in Portofino, Italy.
They initially wed in May following practice nuptials in Las Vegas in March, before holding the third ceremony for family and friends in Italy.