Although we'd still argue that a Green Lantern movie series that doesn't include Hal Jordan, John Stewart and Guy Gardner is missing a great opportunity, a young up-and-comer like Jai Courtney would give the studio plenty of options for solo appearances. After memorable performances in both Jack Reacher (2012) and A Good Day To Die Hard (2013), Courtney is distinguishing himself as a name to know.
Possessing the physicality for action and ability to instill fear with a smile on his face (see: his role in Jack Reacher for evidence), Courtney is about as close to a live-action Gardner as any actor we've seen. He may not have proven himself as a reliable action star just yet, but if introduced as part of a team of heroes in Justice League, or even a Green Lantern Corps film, he has the potential to excel.
Bottom line: if a movie version of Gardner is written without Courtney's name on the short list, the studio is missing out.