Hollywood beauty Scarlett Johannson is worried that her small frame will make her less convincing while playing the deadly vamp, ‘Black Widow’, in her much awaited film ‘Iron Man 2’.

The pint sized blonde bombshell who is considered one of the sexiest woman in Hollywood, said that she was scared her petite frame will be a barrier for her, reported Sun online .

“I wanted to be able to look at something and go, ‘Okay, I’m going to knock the person out’. To believe that is a challenge in itself, especially when you’re 5’3″ and fighting someone who’s seemingly a giant,” said the 23-year-old actress who is married to actor Ryan Reynold.

The actress who is tipped to play screen goddess Marilyn Monroe in a planned bio-pic said that she trained for months to get into the skin tight leather cat-suit that she had to wear in the film.

“I did a lot of stunt training, weight training and all that stuff for Iron Man. It took strength training to try to fit that mould,” said Johannson.