The Chicago set of Transformers 3. (WENN.COM photo)

An extra injured on the set of the new Transformers movie is in a stable condition in hospital after undergoing brain surgery.

Gabriella Cedillo, 24, was airlifted to hospital in Indiana in a critical condition after suffering injuries in a car stunt gone wrong on Wednesday.

Eyewitnesses claim Cedillo was hit in the head by a moving object that went through the windshield of a car she was in during a stunt.

An extra said, "The vehicle was being towed by another vehicle... the cable between the two vehicles broke. It whipped around and sliced through the woman's car and sliced through her skull, apparently."

Cedillo's mother and brother have told a Chicago, Illinois radio station the bank teller is now in stable condition following an operation on Thursday.