This article contains SPOILERS for Justice League.
A scrapped Justice League post-credits scenes originally included two Green Lanterns. Hal Jordan, the second Green Lantern, was one of the original founding members of the Justice League of America when DC Comics introduced the superhero team in The Brave and the Bold #28 in 1960. Green Lanterns have always been founding members of the team throughout each iteration, and they continue to be staples in the overarching DC universe - and that's what made their absence in Zack Snyder's Justice League so prominent.
The DCEU's Justice League was formed by Batman and consisted of Wonder Woman, Aquaman, Cyborg, and the Flash, in addition to the Caped Crusader himself, with Superman joining the team at a later point. Green Lantern nor Martian Manhunter (another original founding member) were anywhere to be seen. However, the Lanterns' existence in the newly-formed shared universe was confirmed by the ancient battle sequence (a story told by Diana Prince to Bruce Wayne), in which a Green Lantern can be seen fighting Steppenwolf and his army of Parademons thousands of years prior to the events of Justice League. What's interesting, though, is that the Green Lanterns were considered to show up in the film's post-credits scene before the idea was scrapped.
An unnamed VFX artist, who worked on Justice League, recently revealed on Reddit (via username LDN_Film) that the film's original post-credits scene showed Kilowog and Tomar-Re visiting Bruce Wayne at his lake house one night. The scene was reportedly shot during principal photography but was scrapped early on and replaced with Justice League's current post-credits scene, which teases an Injustice League team-up.
Although devout comic book readers, as well as Green Lantern fans, may have been disappointed to find out that the DC superhero wasn't included in Justice League - at least not in the present day - many hoped that the film's post-credits scene would at least tease the group's inclusion in a future Justice League sequel. While that didn't happen, DCEU fans know that the universe's guardians will eventually headline their own film. Green Lantern Corps is currently slated to release in 2020 and Warner Bros. recently confirmed the project to be in active development, so it's possible we may get some news on that front in the near future. However, the studio may also alter their plans following Justice League's critical and commercial letdown.
For now, DCEU fans can look forward to James Wan's Aquaman hitting theaters next December, with David F. Sandberg's Shazam! and Patty Jenkins' Wonder Woman 2 both releasing in 2019. Justice League 2 is currently being written, but that project's status may fluctuate depending on how the first installment performs - though it's fair to presume that, judging by Justice League's post-credits scene, the superhero team won't be going cosmic in the sequel.