"The fact is that despite having previous malpractice liability judgments against him, neither the Chargers nor the NFL initiated an inquiry or provided any oversight of the doctor the team selected to provide care for our players," Smith said in a statement released to The Associated Press. "This Article 50 and any subsequent investigations will be initiated when there is credible evidence that calls into question the treatment given to a player and the overall medical care being provided by team selected doctors."
At a pre-Super Bowl news conference, Smith called for Chao to be replaced as team doctor, and the NFLPA filed a complaint.
Quoting a club source it did not identify, the U-T San Diego reported Sunday that three independent doctors "totally exonerated" Chao.
The NFL and the Chargers refused to confirm the report, citing confidentiality.
Chao hasn't returned calls and texts seeking comment.
According to online records, the Medical Board of California is seeking to revoke Chao's license and has referred the case to the state attorney general for possible charges. A complaint alleges gross negligence, repeated negligent acts and failure to maintain adequate and accurate medical records.
Online records also show Chao was found liable of malpractice last summer in a case involving a regular patient, not a Chargers player, with a judgment of nearly $5.2 million. Records also show he has been publicly reprimanded by the board and pleaded guilty to driving under the influence.
In 2010, Chao was investigated by the Drug Enforcement Administration for writing at least 108 drug prescriptions to himself, which violated controlled-substance regulations. However, an attorney for a pharmaceutical company that filled the prescriptions said the drugs provided to the Chargers were for use by the team's medical staff to treat players.
The San Diego County Superior Court's website lists several actions filed against Chao since 1998, including by Ryan Leaf and other former Chargers players. It's unclear if any of the cases resulted in judgments against the doctor.
"The NFLPA will take every step to hold the NFL and its member clubs accountable to provide the care that they are mandated to provide," Smith said in his statement. "Dr. Chao's previous medical liability issues only increases our desire to engage in a thorough and comprehensive credentialing process to determine which physicians are providing care to our players and how they were selected by the teams."