Michelle Trachtenberg was left out of the in memoriam segment of the Academy Awards just days after her shocking death -- and, fans aren't happy about it.

The in memoriam segment -- which kicked off with a touching tribute from Morgan Freeman to the recently deceased Gene Hackman -- paid tribute to many people who did pass away last year ... including Maggie Smith, James Earl Jones and David Lynch.

However, Michelle wasn't included among their ranks ... and, social media users are outraged by the snub.

Some fans used profanity to express their outrage ... while others say it's possible she was left out because she was more of a TV actress -- best known for her roles in "Gossip Girl" and "Buffy the Vampire Slayer."

However, she did appear in some films like "17 Again" and "Harriet the Spy" ... so, she could have been included -- and, it seems like someone dropped the ball here. We've reached out to the academy for answers ... so far, no word back.

Worth noting ... Michelle wasn't the only actor left out. People online are also upset Tony Todd -- the late "Candyman" actor -- was also left out.

As you know ... Michelle was found unresponsive by her mother just last week -- and, first responders pronounced her dead at the scene.

Michelle's family declined the autopsy ... so, it's unclear what exactly caused her death -- though sources did say she recently had a liver transplant.

Michelle's costars -- from Alyson Hannigan and Sarah Michelle Gellar to Ed Westwick and Blake Lively -- paid tribute to her in the aftermath of her death.