Mel B underwent emergency surgery this weekend to treat what she describes as a "severed right hand" and "two broken ribs" after suffering a fall at a friend's home in London Saturday night
Credit: Mel B/Instagram

Melanie “Mel B” Brown underwent emergency surgery this weekend to treat what she describes as a “severed right hand” and “two broken ribs” after suffering a fall at a friend’s home in London on Saturday night.

The Spice Girl posted a picture to Instagram early Monday morning in which she detailed her injury and showed off a massive purple sling.

“Thankyou to all the wonderful nurses dr’s and my amazing surgeon for the care and expertise given to me here at the hospital I’ve been staying at,” she captioned the image. “Suffering 2 broken ribs a severed right hand needing emergancy [sic] care,to having had to have over a 3 hr surgery to repair the damage hence the purple sling,I’ve had to unfortunately cancel my book signing today in NY,I appolagise [sic] to each and everyone one of you who bought there tickets to meet me today.”

She then elaborated on the injuries, writing: “My right arm/hand is all stitched up and I’m trying to keep still to heal my broken ribs,ohh the pain,but I’m in super safe hands with the care of everyone here at the hospital!!!!!”

Her close friend Gary Madatyan confirms to PEOPLE that Brown, 43, was sleeping in the upstairs room of a friend’s house on Saturday night when she attempted to navigate a narrow staircase and ultimately slipped. “She was upstairs and the room was dark,” he said. “Everyone knows one of her eyes does not see 100 percent.”

Despite her former husband Stephen Belafonte‘s claims that Brown’s drug and alcohol use made her a danger to her children, Madatyan rebuffed any speculation that substances played any role in her accident, providing PEOPLE with documents showing the singer’s clean drug test results from Dec. 6. “She’s not a drug addict; she’s not an alcoholic. It’s just nasty what people are saying,” he said.

In September, Brown agreed to undergo random drug and alcohol testing as part of her custody battle with Belafonte. “Her last drug test happened just a day before the fall, an eight-hour, 10-panel test from L.A. drug center. She’s passed 14, 15 tests already; all of this because of lies he’s told the courts,” Madatyan alleged. “She was coming back the next day to do the drug test [before heading to the] book signing in New York.”

Brown’s Spice Sisters (minus the LA-based Victoria “Posh” Beckham) paid a visit to her bedside and posed for boomerangs — an unexpected precursor to their upcoming reunion in 2019.

“She’s in a lot of pain, but she’ll be fine. She just needs some time to heal,” Madatyan tells PEOPLE.