The references are quite subtle, but could come full circle once Eternals is released.
Furthermore, a space ship that looks quite similar to a vessel belonging to the Celestials can be spotted in a quick shot in Thor: Ragnarok.
The Eternals are the result of a manipulation of the evolutionary process on Earth by the godly alien race of Celestials, whom you may recall were mentioned in The Collector’s (Benicio del Toro) crash course in the history of the Infinity Stones in Guardians of the Galaxy and in its second volume when Ego (Kurt Russell) refers to himself as a Celestial when describing his origins to his son, Peter Quill (Chris Pratt), and his friends.