In 2267, Greenberg was shot and wounded protecting Max Eilerson when some of the crew became possessed by mind-altering aliens. He was later pronounced paralyzed and brain-dead by Dr. Sarah Chambers. Max was greatly affected by the sacrifice of Greenburg, stating that nobody had ever saved his life like that before.
When Captain Gideon went to meet the possessed crew, Eilerson figured out that Gideon wanted them to depressurize the deck, forcing the intelligence back into one body. The alien consciousness was tricked into entering Greenberg's body, which was left available for the aliens to use per Max's suggestion.
Still feeling guilty over Greenburg's willing sacrifice, Max asks Dr. Chambers if they did the right thing in using his body like that, wondering if he would have approved. Max draws some comfort form the fact that Greenburg's death save the entire crew and not just Max alone.
After the crisis, Gideon dictated a message to Greenberg's mother, telling her of her son's bravery and self-sacrifice.