The 39-year-old bantamweight had been ahead on the scorecards before blacking out without an obvious knockout blow, with Teixeira saying the brain "shut down" as a defense mechanism.
Barcelos was taken from the Las Vegas bout on a stretcher, and his corner initially feared a head clash or a heart or neurological problem before hospital tests identified the swelling.
Three days later, Barcelos was discharged, but Teixeira said more testing is needed before any decision on whether he can resume his MMA career.
Teixeira also criticized referee Herb Dean for stopping the fight only after Rosas Jr. stopped punching, renewing his calls for Dean to retire.