The actress made the startling revelation this weekend, responding to a comment someone left on her recent IG post recapping a quarter of the year through 2022 ... which was pretty eventful for her, it seems.

Somebody innocently wrote, "Can't wait to see what you'll be wearing on Oscar night," which prompted a couple different responses from her -- one which stated she actually hadn't been invited ... and another revealing just what her plans were for next Sunday.

Rachel first wrote, "i'm not invited so sweatpants and my boyfriend's flannel." She followed up with a bit more elaboration afterward, explaining that she tried making it happen (being able to attend, that is) but was met with resistance.

She adds, "i hope some last minute miracle occurs and i can celebrate our film in person but hey, that's how it goes sometimes, i guess." RZ went on to thank her fans for all the shock and outrage -- and yes, there certainly has been some online on her behalf -- going on to say she's also disappointed.

It's unclear why Zegler might've been snubbed, especially since her costar -- Ariana DeBose -- is a bona fide favorite to win Best Supporting Actress, and not just that ... but Spielberg himself is up for Best Director. The film itself is even up for Best Picture for crying out loud.

Of course, the Academy has yet to release an official list of who's expected to attend, keeping all those logistical deets hush-hush a week out. So this is eye-opening, for sure.

COVID might be to blame, but seeing how Zegler was literally the lead of 'WSS' ... you gotta figure they could've squeezed her in somewhere if they wanted. Yes, not everyone from 'West Side Story' can attend -- it's a massive cast -- but the main people certainly can, no???

Also strange is the fact that Zegler was able to attend two other major movie award shows this year ... albeit both were across the pond. She went to the Critics Choice Awards and the BAFTAs (both of which were in London on the same day) ... but somehow, is missing the Academy Awards, which is by far the biggest of them all.

If the seating arrangement isn't finalized at this point, then the Oscar planners should definitely reconsider extending an olive branch -- because yeah, this feels like BS.

BTW, even though Spielberg's offering bombed at the box office ... it was actually high-key fantastic, from the set design to the cinematography and especially in the hair/makeup and choreography departments.