Alicia Silverstone fears being overshadowed by Britney Spears. The "Clueless" star has opted out of guest starring in "How I Met Your Mother" because the pop singer is also starring in the same episode, it has been claimed.

Silverstone was supposed to play a hot doctor that lead star Ted, played by Josh Radnor, has a serious crush on. But apparently, the 31-year-old actress bailed out after learning the doctor's receptionist will be played by Spears, which might possibly overshadow her.

Reports suggest that her role is now being filled in by "Scrubs" actress Sarah Chalke.

Meanwhile, the show's creator Craig Thomas reveals to Usmagazine.com the "Toxic" singer had laughed a lot at the episode's table read.

He replied when asked how did the cast gett along with her, "Great, they seemed to click. She seemed to fit right in! She was having a good time. She was laughing.

"Everyone was having a good time, and I think she had a good time."