'Price Tag' sensation Jessie J has been forced to cancel her appearance at Ponty's Big Weekend after being diagnosed with a viral infection.

The songstress was due to perform at the event later tonight (July 20), but took to social networking site Twitter earlier this afternoon to apologise to her Heartbeats for not being able to make the date as she has to follow the doctor's orders:

"I want to personally apologise to all my fans who would be going to my show tonight (Pontys Big.W) I have been diagnosed with a viral infection recently that has caused me to be extremely fatigued."

"I was hoping to be better but I have been to see my doctor this morning after not feeling great who has advised me I am still in need of rest & to perform will make me worse. I hope you can all understand that I wish I could be there. But I'm just not well enough. Back to bed I go :( So sorry x."

When talking about her plans for a charity head shave recently, Jessie J revealed that she's excited to see her natural hair colour again after so long:

"I think I'm going to love it. My hair grows so quick, but it's naturally dark blonde. Seeing my natural roots will be interesting."

Watch her stunning New York City subway performance of 'Who You Are' below: