Updated

(SportsNetwork.com) - The NFL Players Association thinks Tampa Bay coach Greg Schiano leaked confidential information about former Buccaneers quarterback Josh Freeman's inclusion in the NFL's substance-abuse program, according to a report.

The union wants the league to participate in a joint investigation of Schiano so it can question him, USA Today reported Sunday, citing a correspondence it had obtained.

Previously, NFLPA head DeMaurice Smith said the union would investigate if the Buccaneers leaked information about the quarterback.

The union says it doesn't have confidence in the league's separate probe partly because it is unaware of any previous NFL investigation into such a confidentiality breach that has yielded discipline, according to the report.

After ESPN reported the quarterback's inclusion in the drug program, Freeman said in a statement he never tested positive for an illegal drug but takes ADHD medication and said he accidentally took Ritalin instead of Adderall last year, which triggered a positive test.

As a result, he was placed in Stage 1 of the NFL's substance-abuse program and submitted to frequent drug tests.

Freeman was released by the Buccaneers after being benched by Schiano and now plays for the Minnesota Vikings.

Schiano was asked by reporters if he was the source of the leak and replied, "absolutely not."

The NFLPA says it has information Schiano discussed Freeman's inclusion in the drug program with other Buccaneers players, according to USA Today.

An NFL spokesman told the paper the league takes the confidentiality provision of the drug policy "as seriously as the union and will vigorously pursue any leads the union provides."

"However, such information should be shared confidentially with our office rather than inappropriately leaked to the media before the investigation has been concluded," spokesman Brian McCarthy said.