The 30-year-old Australian singer and experienced equestrian, who is best known for songs such as 'Mr Mysterious' and 'XX', was riding with friends at her Victoria property when the accident occurred.
According to the Herald Sun, Amarosi's companions took her to hospital and she discharged herself 12 hours later. However, she began to feel unwell the next day and returned to the medical centre, where she was kept in for suspected internal injuries.
The musician is now expected to spend the next week under observation and was forced to cancel her twilight concert at Melbourne Zoo on Saturday night (February 25).
She told her fans: "I am really sorry to everyone who was coming to the twilight show. I was really looking forward to performing to you all in such a great environment, especially as this was planned to be my last Melbourne show before heading back to Los Angeles."
Amarosi was with Australian TV star Molly Meldrum, working on vocals for a new song, just hours before his near-fatal fall at his Melbourne home before Christmas. He is still recovering from various injuries in Epworth Rehabilitation Centre.
> Vanessa Amarosi: 'I've finally opened up to fans'
> Vanessa Amorosi: 'I've come of age as a singer'
Watch Vanessa Amarosi's 1999 video for 'Absolutely Everybody' below: