Karen Gillan has shaved her head for 'Guardians of the Galaxy'.

The 'Doctor Who' star - who is best known for playing the Time Lord's feisty sidekick, Amy Pond, in the British sci-fi series - has gone bald in order to play brutal space pirate, Nebula, in Marvel's big-budget superhero film.

The 25-year-old actress unveiled her new style at Comic-Con in San Diego, California, where she arrived wearing a flame-haired wig, which appeared to be her normal tresses, before whipping off the hairpiece to reveal her new appearance.

She then told the crowd: ''It's liberating. I think everyone here should shave their heads.''

Chris Pratt is also on board for the motion picture as the group's leader, the Star-Lord - who is also known as Peter Quill - while Zoe Saldana will play superhuman vixen Gamora, and Dave Bautista is set to portray muscular henchman Drax the Destroyer.

The film - which will be directed by James Gunn - is scheduled for release in August 2014 but Zoe admits they still have ''85 per cent of the movie left to shoot.''

She said: ''This is sort of like the anti-hero hero movie. We're meeting these characters, they're thieves, they're rebels, they're assassins, and they're going to be learning very big lessons.''