She has cancelled a book signing in New York after suffering two broken ribs and an injury to her hand in the accident.
The Spice Girls star said she needed three hours of surgery to repair damage to her hand, which has resulted in stitches.
She shared a photograph of her arm in a purple foam sling and wrote on Instagram: "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, suffering 2 broken ribs a servered right hand needing emergency 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 apologise to each and everyone one of you who bought there tickets to meet me today.
"I'm absolutely gutted but I can assure you it WILL happen at a later date, I promise, but for now my right arm/hand is all stitched up and I'm trying to keep still to heal my broken ribs.
"Ohhh the pain, but I'm in super safe hands with the care of everyone here at the hospital!!!!! Thank you all for understanding, I love you all." [SIC]
She added the hashtags "#accidentshappen" and "needtimetoheal".
Mel B's book, Brutally Honest details her battles with drugs and the domestic abuse she has suffered over the years.
Last month the star visited a refuge in Leeds as part of her work with Women's Aid where she spoke about her suicide attempt after suffering years of abuse.
She said: “I was living a completely double life. There was my life was on TV, I was filming America’s Got Talent and living a complete hell. And I felt embarrassed by that.”