The actress stepped into the Lovelace role at the last minute, when original star Demi Moore dropped out of the biopic because of her recent hospitalisation.
Parker has now admitted to Access Hollywood that she had very little time to prepare for the movie.
"It was difficult because, obviously, the circumstances are not ideal," the actress said. "I obviously conveyed that to the filmmakers [and] that I was aware and I was sorry for the reasons that they had to reach out to me."
Parker continued: "Also, of course, the somewhat daunting task of playing somebody with very little time [to prepare for] who was obviously such an important person in the women's movement, but also played such a pivotal role in Linda's life."
The actress recently revealed that she banned former Sex and the City co-star Chris Noth – who also appears in Lovelace - from visiting her on the set.
Lovelace - which also stars Amanda Seyfried as porn star-turned-activist Linda Lovelace and James Franco as Hugh Hefner – is expected to be released later this year.
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