American boxer Patrick Day died on Wednesday in Chicago as a result of the traumatic brain injury he suffered during his fight on Saturday, where he was knocked out by Charles Conwell in the 10th round.

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.

"Patrick Day passed away today, October 16, 2019, succumbing to the traumatic brain injury he suffered in his fight this past Saturday, October 12, at the Wintrust Arena in Chicago, IL," his promoter Lou DiBella said in a statement.

"He was surrounded by his family, close friends and members of his boxing team, including his mentor, friend and trainer Joe Higgins."

"On behalf of Patrick's family, team, and those closest to him, we are grateful for the prayers, expressions of support and outpouring of love for Pat that have been so obvious since his injury."

Day was rushed to the hospital on a stretcher after Conwell landed a flurry of punches that left him motionless on the canvas.

Before turning professional, Day was a highly decorated amateur who won two nationals titles.

He turned pro in 2013 and became a world-rated super welterweight contender, capturing the WBC Continental Americas championship in 2017 and the IBF Intercontinental championship in 2019. In June he was rated in the top-10 by both the WBC and IBF.

Day's death comes after 23-year-old Argentine super lightweight Hugo Santillan died in July from injuries suffered in the ring and 28-year-old Russian Maxim Dadashev passed away two day earlier from brain injuries during his fight.

"It becomes very difficult to explain away or justify the dangers of boxing at a time like this," DiBella said.

"This is not a time where edicts or pronouncements are appropriate, or the answers are readily available. It is, however, a time for a call to action.

"While we don't have the answers, we certainly know many of the questions, have the means to answer them, and have the opportunity to respond responsibly and accordingly and make boxing safer for all who participate."