Knox, 26, served four years of a 26-year sentence in an Italian prison for the murder of Meredith Kercher, whose half-naked body was found in a pool of blood in the house she shared with the American student.
After an appeal, Knox and her Italian ex-boyfriend Raffaele Sollecito were acquitted in 2011 of the crime prosecutors attributed to a sex game gone wrong.
Knox then returned to her home near the northwestern US city of Seattle.
"She will not be returning to Italy for the retrial," her lawyer David Marriott told AFP.
"She is not required to be there and had never agreed to attend."
In March, Italy's highest appeals court overturned the acquittal and ordered a retrial in a Florence appeals court, citing "numerous examples of shortcomings, contradictions and incoherencies" in the original appeal ruling.
It said the jury that acquitted Knox had not considered all the evidence.
The only person behind bars for the murder is Rudy Guede, a local drifter born in Ivory Coast who is serving a 16-year prison sentence after being tried separately and convicted of murder and sexual assault.
Based on the physical evidence, prosecutors say the murder could not have been carried out by one person.