Day, 27, had been in a coma for four days following his defeat and, despite having emergency brain surgery at Northwestern Memorial Hospital, doctors were unable to save the junior middleweight.
Check out India's report card on the fourth day of the 2016 Olympics.
India's Vikas Krishan out-punched American Charles Conwall to win his middleweight (75kg) preliminary bout 3-0 at the Rio Olympics on Tuesday.
An American ended his Olympic dream in 2012 amid controversial circumstances and Vikas Krishan will have redemption on mind when he takes on another American Charles Conwell in his opening bout to kick off India's boxing campaign in the Olympic Games, in Rio de Janeiro, on Tuesday.
Archer Atanu Das and boxer Vikas Krishan entered the pre-quarterfinals, while the men's hockey team stood up to the challenge posed by Argentina to virtually sew up a last-eight spot on a reasonably successful day for Indian athletes in the Olympic Games in Rio de Janeiro.
Just one win away from winning an Olympic medal after a comprehensive victory over his opponent in his pre-quarterfinal bout, Indian boxer Vikas Krishan says he wants nothing less than a gold in the Rio Games.
A tough draw will put their grit to test when the three-member Indian boxing team begins its Olympic campaign, aiming to lift the gloom that pervades the sport back home owing to the long-standing administrative mess.