Winona Ryder’s doctor could be in big trouble!

Authorities charge that he gave the problem-plagued actress the powerful painkiller Oxycodone without a prescription.

“The doctor’s action is the subject of an ongoing investigation,” L.A. County Deputy D.A. Ann Rundle told The ENQUIRER.

“He has made a declaration, under penalty of perjury, that he supplied drugs to Winona Ryder without a prescription.”

The “Girl, Interrupted” star’s problems with the law began when she was busted before Christmas and charged with stealing clothes worth $6,000 from Saks Fifth Avenue in Beverly Hills.

The 31-year-old actress had originally been charged with four offenses, all felonies: grand theft, vandalism, second-degree burglary and drug possession.

On October 16, L.A. County Superior Court Judge Elden Fox dismissed the felony drug possession charge against Ryder.

Deputy D.A. Rundle had recommended the dismissal, saying that Ryder “lacked criminal knowledge” needed for a conviction, because her own doctor gave the Oxycodone painkiller pills to her.

The trial date on the other charges was scheduled for October 24.

Outside the court, the star’s attorney Mark Geragos thundered that the dismissed drug charge had been “totally unnecessary” in the first place.

“Right after she was arrested, we gave the prosecution a prescription Winona had for the pills, prescribed after she broke her elbow,” said the lawyer.

But Deputy D.A. Rundle insisted: “Nobody supplied a prescription for Oxycodone (the generic version of the pills for which she had a prescription).

“In the end, the doctor made a declaration that he supplied the pills to Miss Ryder without a prescription.”

Attorney Geragos said his client took some free samples of the generic version of the painkiller from her physician but added, “The worst thing that can be said of Winona is that she was trying to save a couple of bucks.”

The district attorney’s office would not reveal the name of the physician.