Day, 27, was knocked out in the 10th round of his super-welterweight bout in Chicago on October 12 and fell into a coma, with his promoter confirming Day's death on Wednesday, reports The Guardian.
"He was a son, brother, and good friend to many," said a statement from Day's promoter Lou DiBella.
"Pat's kindness, positivity, and generosity of spirit made a lasting impression with everyone he met. Patrick Day didn't need to box. He came from a good family, he was smart, educated, had good values and had other avenues available to him to earn a living.
Day was rushed to the hospital on a stretcher after Conwell landed a flurry of punches that left him motionless. He underwent emergency brain surgery at Northwestern Memorial Hospital but the doctors couldn't save the American boxer.
Following the tragedy, Conwell had written an open letter on Tuesday. "This is my last time speaking on the situation because of this being a sensitive topic not only for his family and friends but for myself and the sport of boxing," Conwell said.
"Dear Patrick Day," Conwell wrote. "I never meant for this to happen to you. All I ever wanted to do was win. If I could take it all back I would. No one deserves for this to happen to them. I replay the fight over and over in my head thinking what if this never happened and why did it happen to you. I can't stop thinking about it myself. I prayed for you so many times and shedded so many tears because I couldn't even imagine how my family and friends would feel.
"I see you everywhere I go and all I hear is wonderful things about you. I thought about quitting boxing but I know that's not what you would want. I know that you were a fighter at heart so I decided not to but to fight and win a world title because that's what you wanted and that's what I want so I'll use you as motivation every day and make sure I always leave it all in the ring every time. #ChampPatrickDay. With Compassion, Charles Conwell."
( With inputs from IANS )