At the end of Captain America: Civil War we watched The Winter Soldier go back into a suspended animation state. While the future of the character became an open question, we now have an idea when he'll be released from his coma. While we could have seen Bucky's return in any number of upcoming Marvel films, it appears the plan is to leave him on ice until Avengers: Infinity War.
While the fate of most of the MCU characters was left up in the air following Captain America: Civil War, Bucky Barnes, aka The Winter Soldier, was actually left in a state that could have given us a hint as to where he'd turn up next. His body is currently being studied by scientists in the African nation of Wakanda, the home of T'Challa, the Black Panther, as they try to figure out how to deprogram him. This led us to at least entertain the possibility that we might see him in early 2018 when the Black Panther movie hits screens. However, an article on Sebastian Stan in The Hollywood Reporter notes that the next MCU movie he'll be filming will be Avengers: Infinity War in early 2017. Since Infinity War hits after Black Panther, this would imply that Stan won't be doing any filming for that one.
We didn't really expect to see The Winter Soldier before 2018. While there are numerous Marvel movies planned between now and then, it didn't make much sense for the character to somehow show up in Thor: Ragnarok or Spider-Man: Homecoming. Of course, just because Avengers: Infinity War is the next movie Sebastian Stan is working on for Marvel, it doesn't completely close the door on a possible Black Panther cameo. There are only three months in between the release date for the two films, and both are scheduled to begin filming in "early 2017." The filming of Infinity War is expected to be a massive undertaking, considering the number of characters that are expected to make an appearance. It wouldn't be surprising for the filming of Infinity War to actually start prior to Black Panther simply due to the scope of the production. It will likely take longer to produce.
What's more, if all they needed from Sebastian Stan for Black Panther was a simple cameo, like a post-credits stinger, they could easily film that as part of his responsibilities for Infinity War rather than having him make a separate trip to the Black Panther set. Again, the two are happening so close together, one scene shot later wouldn't impact production in the slightest. DC recently did something very similar for Suicide Squad.
Until we know otherwise, we can take this at face value, and assume that The Winter Soldier will spend all of Black Panther unconscious, and just off screen. Would you like to see Sebastian Stan return prior to Avengers: Infinity War? Let us know in the comments.