In most iterations of the Justice League's beginnings, whether it's in the comics or another form of media, a Green Lantern has usually been one of the team's founding members. That won't be the case in the Justice League movie next year. When Superman, Batman, Wonder Woman, Flash, Aquaman and Cyborg team up to fight the forces of evil next year, they'll lack an emerald light to illuminate the way for them. Over the last year, it's been implied that Green Lantern won't be involved in Justice League, but now there's word that the Green Lantern mythology may play a role in the movie after all.
Buried in a report citing all of main elements about Justice League that we know so far, The Wrap mentioned that a member of the Green Lantern Corps will appear during a "key sequence." No other details were provided, but before some of you get too excited, keep in mind that the Green Lantern Corps is thousands strong (7200 when there's two of them assigned to a sector). Just because a Green Lantern could show up doesn't mean that it will be Hal Jordan, John Stewart or one of the primary Emerald Knights from Earth. It could just end up being a regular, not-famous member of the Corps who pops in for a bit. Regardless, should this tidbit of information prove true, this would be the first Green Lantern reference/appearance in the DC Extended Universe.
So if a Green Lantern does show up in Justice League, how might it happen? Two ideas come to mind. Assuming that this member is someone unknown rather than notable, maybe this particular Lantern comes across Steppenwolf, one of Darkseid's chief minions from Apokolips. The Green Lantern Corps are essentially the intergalactic "beat cops" of the DC universe, so it's plausible that one of its members comes across Steppenwolf and his Parademon army at the beginning of the story while on patrol, and they're subsequently eliminated. This would show moviegoers how powerful the Apokoliptan general is. The second potential option was a rumor reported almost two years ago, where one of the main Earth Green Lanterns will show up at the end of the movie to set up 2019's Justice League 2, possibly to warn the heroes about Darkseid. This sequence may not be as action-packed, but it would lay groundwork for the DCEU's future.
After numerous appearances in animation, video games and that unfortunate Justice League of America 1997 pilot, Green Lantern was finally brought to the big screen in 2011, but because the Ryan Reynolds-led movie was critically panned, Warner Bros opted to reboot the property for the DCEU. As it officially stands now, Green Lantern Corps will arrive on July 24, 2020, and it's been reported we could see as many as three Earth Lanterns star in the movie. Whether any of them appear before that remains to be verified.
Justice League hits theaters on November 17, 2017.