Junior middleweight Charles Conwell understandably has the injured Patrick Day on his mind day and night.

Conwell knocked Day out in the 10th round of their bout on Saturday night's Oleksandr Usyk-Chazz Witherspoon undercard at Wintrust Arena in Chicago. Day, who had been knocked down twice earlier in the fight, did not regain consciousness.

He was rushed to Northwestern Memorial Hospital, underwent emergency brain surgery and remains in a coma, with his team saying doctors hold out little hope that he will survive.

While Day's family has gathered at his bedside, Conwell wrote an open letter to Day on social media, first saying, "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."

Then Conwell let flow his emotions about the situation.

"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."

Conwell (11-0, 8 KOs), a 21-year-old blue-chip prospect from Cleveland and a 2016 U.S. Olympian, was matched with Day (17-4-1, 6 KOs), 27, of Freeport, New York, a former amateur standout in his own right, with the idea that Day would give Conwell the first serious test of his career even though Day was coming off a hard-fought decision loss to Carlos Adames, another up-and-coming fighter, on June 28.

Lou DiBella, the promoter of Conwell and Day, told ESPN on Tuesday night that he was blown away by what Conwell wrote.

"No one prompted him to write it -- not his management and not his promoter," DiBella said. "I know Charles is profoundly sad right now by what happened. I'm trying to make him realize it's no fault of his. I read what he wrote and it put a tear in my eye. It was an incredibly human and honest and genuine response from a kid who is just 21. He's a really good kid, a really good person. I think it was very obvious to both of them that they were both good guys. Charles' letter was really touching. It screams of honesty and authenticity."

DiBella was also impressed by the reaction to Conwell's letter from Joe Higgins, Day's longtime trainer who is very close to Day.

"I thought the response from Joe Higgins was beautiful," DiBella said.

After Conwell posted his letter, Higgins, who remains in Chicago with Day and his family, responded in his own social media posts.

"I just wanted you to know that we do understand what you must be going thru as well," Higgins wrote to Conwell. "As devastated as we are we realize you are equally devastated. We know if it was the other way around we would be just as distraught. Thank you for your kind words. Patrick was born across the street from me so our relationship is special. He would have wanted you to continue. I am rooting for you to reach your dream, the same one he had. God Bless your team and we will keep you in our prayers as well.

"I too am distraught because I feel responsible but do realize there is no fault. Stay strong and please don't think we blame you. Best wishes going forward and please continue to pray for Patrick. You guys are warriors, but humble and that's what makes you special."