'Thor: Ragnarok' Cast News & Spoilers: Which Three Characters From Original Cast Are Unsure Of Returning? Find Out Why Here!

"Thor: Ragnarok," the third film in the "Thor" franchise in the Marvel Cinematic Universe, isn't hitting theaters until 2017. However, there are already reports that three of its characters might not be back for this latest installment for three different reasons.

Jaimie Alexander, who played Sif in the "Thor" movies, revealed she's not 100 percent sure she's going to be in "Ragnarok" due to the script changes. "I am literally in limbo," the actress told Comic Book Movie. "I would love to do it, but whether or not it's going to work on my short hiatus from 'Blindspot' I'm not sure."

Deadline reported in November that Alexander's TV show, "Blindspot," has received a second season renewal from NBC, which means that she will only have a break from filming episodes during the hiatus season in the summer. At the moment, filming details for "Thor: Ragnarok" have not even been revealed, so there's a strong possibility Sif will not figure in the third story.

Also confirmed not returning in the third installment are actors Stellan Skarsgard and Idris Elba. Skarsgard, who played the scientist Dr. Eric Selvig on "Thor," revealed he's known ahead that he is not going to be in "Ragnarok," based on his five-picture deal with Marvel. "Thor 3 is not on my slate," he told Den of Geek. He already appeared in four Marvel films in his contract and he's still going to be in the third "Avenger" film.

On the other hand, Elba's reason for sitting out "Thor: Ragnarok" is plot-related. His character, Heimdall, who is the gate keeper of Thor's mystical land of Asgard, will supposedly meet his death early on in the film. This will roll out part of the storyline that will trigger Thor to battle with Hela, played by Cate Blanchett, per Geek.

However, Elba previously expressed he didn't enjoy working on "Thor" and his character's death might just be what he wanted. "I was in this stupid harness, with this wig and this sword and these contact lenses," he told Telegraph. "It ripped my heart out."