The 23-year-old fell off a stage during recent rehearsals for a show and was diagnosed with having ripped ligaments.
She then appeared on stage with a cast on her foot and sat on a throne for her performance but she has now revealed that her foot is actually broken.
The star wrote on Twitter: 'I am back in the UK. I didn't tweet all day yesterday as I was at the hospital having scans on my foot! To get a specific diagnosis.
'Turns out I've been hobbling around with a broken foot. So will be in a hence grey darfaydar looking boot and on crutches for 6 weeks (cool lol).'
Jessie J is set to play on the Other Stage at the festival on June 25.