However just like she found with Lawrence, the 20-year-old actress - who plays Jean Grey in the upcoming mutant movie - soon realised her fears were unfounded.
She says Fassbender has a great sense of humour.
"I looked over and he gave me the middle finger, jokingly, and I thought, 'We're going to get on,"' Turner said of her first day on set with Fassbender.
She now looks set to hit the big time after landing the role of Jean and confessed she couldn't stop crying when she won the part. Although she's quickly carving out a successful career in Tinseltown, she still finds herself getting star-struck around her favourite actors.
When quizzed about the funny photograph she posted while sitting in front of Ryan Gosling at the Screen Actors Guild Awards earlier this year (16), Sophie recalled she couldn't keep her cool while being in such close proximity of the heartthrob.
"That was one of the greatest moments of my life," she laughed. "I'm now terrified that I'm going to do a project with him, though. Maybe he's seen the Instagram... I always do this. I'm never cool around celebrities."