Unfortunately, Kevin Feige refused to shed more light on Captain Marvel in his interview with MTV.
Hopefully more will be revealed about Captain Marvel soon as we inch closer and closer to the March 2019 release date.
Who that someone is, and how his eye was lost, have not yet been revealed in the MCU, but it seems that may be happening in Captain Marvel.
It has never been established in the MCU how Nick Fury lost his eye, although he does tell Steve Rogers in Captain America: The Winter Soldier that, “The last time he trusted someone, he lost an eye.”