Jessie J has promised to "make it up" to her fans for cancelling a string of appearances after she broke her foot in two places last month.
The star needed surgery on Thursday and was ordered to rest after having the operation.
Among the shows affected are T In The Park, Lovebox and the iTunes festival.
Continue reading the main story
I was so excited about the summer and I'm as upset as you all are. But unfortunately these things happen. I have to remain positive and I promise I will make it up later in the year
She said: "Sorry doesn't feel enough to say, I am devastated for my fans that I know have been waiting to see me and working hard for tickets."
Her injury didn't stop the singer performing at Glastonbury last weekend.
Jessie J ignored doctors' advice to skip the festival and performed through the pain as she appeared on a specially-made gold throne on The Other Stage.
T in the Park festival director Geoff Ellis said: 'I am gutted. She was someone I was really looking forward to seeing and I'm sure a lot of T in the Parkers were too.
"We wish her a speedy recovery and hope to welcome her next year."
The star found out she had a broken foot last Thursday, two weeks after falling off a stage platform while rehearsing for a London concert.
She was originally told that she had ripped a ligament.
"I was so excited about the summer and I'm as upset as you all are," she added.
"But unfortunately these things happen. I have to remain positive and I promise I will make it up later in the year."
In a tweet she added: "I'm still in hospital. I had major surgery not a in and out thing in alot of pain still."
Jessie J begins her own headline tour in October.
She's then supporting Katy Perry on her California Dreams US tour in November.
The singer went to number one earlier this year with her single Price Tag featuring American rapper B.o.B and also topped the BBC's Sound of 2011.