Harry Morton went under the knife to repair a deviated septum just weeks before his death -- and we're told authorities are looking at this as one scenario that could have caused his death.

Sources close to Morton tell us he recently got a septoplasty -- a surgery designed to straighten out the septum to allow for better airflow through the nose. Here's the scenario ... if the surgical instruments go deeper than they should, it could end up damaging the base of the brain ... something that could lead to death.

There's no way of knowing precisely what caused Harry's death until an autopsy is performed ... that will occur Monday. What's more ... our sources say Harry was back to his normal routine and as far as we could determine, he never complained about complications from the surgery.

As for other theories ... our law enforcement sources say there were no illegal drugs found at the scene and only a couple prescription drugs. There are other possibilities as well ... that would result in the death of an apparently healthy 38-year-old male, but so far, no answers.

TMZ broke the story ... Morton was found unresponsive by a family member at his home in Beverly Hills on Saturday. He was pronounced dead at his home.

Harry's ex, Lindsay Lohan, posted a photo of the couple in their heyday on Sunday, captioning the post, "Best friends. Best life."

Harry was best known as the founder of the Pink Taco restaurant chain, which became a big hit on the Sunset Strip and has since expanded to other cities. His grandfather, Arnie, cofounded the incredibly popular Morton's The Steakhouse chain in 1978, and his dad, Peter, cofounded the Hard Rock Cafe empire in 1971. Harry worked at HRC for years and later headed up the business' development wing.

He was also a volunteer sheriff's deputy in and around L.A. and dedicated hundreds of hours a year to the department. Morton was recently honored as Reserve Detective of the Year.

Harry was 38.

RIP