Attorney Joseph Mannis wrote about the "Easy Rider" star's grave condition in a declaration filed Wednesday asserting the actor cannot be questioned by his wife's attorneys in a deposition.
The prognosis contradicts previous filings in the divorce proceedings that were bullish about Hopper's recovery chances.
Hopper, 73, and his wife, Victoria, have been locked in a bitter feud since the actor, director and artist filed to end the couple's nearly 14-year marriage in January.
He weighs barely 100 pounds and was described by his physician Dr. David Agus in the court filing as extremely weak and unable to carry on long conversations.
Agus states that undergoing a deposition "could actually threaten his ability to survive his current health crisis."
The doctor added, however, that he approved an appearance Friday by Hopper to receive a star on the Hollywood Walk of Fame because it is likely to be a positive experience.
A phone message seeking comment from Victoria Hopper's attorney, Sorrell Trope, was not immediately returned. Mannis did not return a call seeking further comment.
Hopper filed a declaration last month saying he was undergoing promising chemotherapy treatments and remained hopeful "that this treatment will be successful so that I may soon resume the full enjoyment of my life and work."
Dennis and Victoria Hopper have agreed to stay 10 feet away from each other while the divorce is ongoing. She has stated in court filings that Hopper filed for divorce to cut her out of her inheritance, a claim the actor has denied.
The case is scheduled for a court hearing on April 5.