The 47-year-old actor was shooting battle scenes for the horror apocalypse movie in Glasgow with 700 extras when the actress fell to the ground in the melee.
Pitt quickly scooped her up in his arms and put her back on her feet before she faced the risk of getting badly injured.
"Lots of people hurt themselves and Brad (Pitt) came to the rescue of one woman who slipped. I don't think she could believe it when Brad picked her up. He didn't have time to speak to her as it was mid-shoot. But she said afterwards how grateful she was, despite having a grazed knee," femalefirst.co.ukquoted a source as saying.