The scene depicts Tony Stark floating through space after the battle with Thanos. In one shot, Groot’s wooden face does seem visible, meaning he would be seated behind Stark.
While it’s possible that Groot is onboard, the beginning of the trailer makes it seem as though Stark is all alone, “adrift in space with zero promise of rescue.” The not-quite-clear image could also very easily be one of the vessel’s headrests with some very convenient shadowing.
The first live-action appearance of Groot was in 2014’s Guardians of the Galaxy. The gentle giant won over fans, then devastated them with his death in the film. The final scenes showed that a baby Groot had been planted, which meant he could live on in a new form.
Guardians of the Galaxy Vol. 2 featured an adorable Groot, who had only aged to be a toddler. Then, fans saw Groot utter one final “I am Groot,” before he was wiped away by Thanos’s snap at the end of Infinity War (click here).
It’s doubtful that Marvel will give away much in any forthcoming trailers, so fans will have to wait until the movie hits theaters on April 26, 2019 to know for sure.