EXCLUSIVE

NHL officials have been notified that the Royal Canadian Mounted Police investigation into ex-L.A. Kings player Mike Richards involves the prescription drug oxycodone ... multiple sources tell TMZ Sports.

Our sources say Richards was stopped while crossing from the United States into Canada on June 17th ... and we're told he was questioned about oxycodone pills, a powerful painkiller.

For the record, Richards has NOT been charged with a crime.

However, he has since been cut from the team for "a material breach of the requirements of his Standard Player's Contract."

We reached out to Richards' agent for comment multiple times but haven't heard back. Canadian officials refused to comment, citing privacy laws.