The blonde beauty has been busy with interviews and premieres to raise the profile of the new sci-fi thriller, which debuted at number two on the U.S. box office chart over the weekend (19-20Feb11), with takings of almost $20 million (£13 million).
But her constant talks about the movie have left her battling a sore throat - which is proving problematic for recording her scenes as school cheerleader Quinn in new installments of the all-singing, all-dancing show.
She tells Interview magazine, "This past month... We've been filming during the week and then doing quite a few junkets on the weekends for I Am Number Four. It really just happened (losing my voice), two weeks ago was the first time.
"Now, the mentality is to rest your voice at any opportune moment. I went to the recording studio and I've never had this - I couldn't sing. It sounded completely unnatural, like I had a frog in my throat. And I kept saying, 'I'm just so sorry, I'm just so sorry.' It just keeps coming and going.
"There's been a couple of scenes where I can't even... Quinn's voice is higher, and it's got this pitch to it. You're going to be able to tell. I just couldn't do it... It will come back one of these days."