Boxer Patrick Day has died from severe brain injuries after a brutal knockout.

He was 27.

Day was taken to Northwestern Memorial Hospital Saturday night, after his 10th-round loss to Charles Conwell. He remained there until Wednesday, when he died, according to CBS News.

"He was surrounded by his family, close friends and members of his boxing team, including his mentor, friend and trainer Joe Higgins," promoter Lou DiBella said in a written statement.

After the knockout loss, Day remained down for several minutes. He was unconscious as an ambulance took him to the hospital, experiencing several seizures along the way.

Day underwent surgery for his injuries at Northwestern Memorial, CBS News says, and remained in critical condition until he died.

After hearing of Day's death, Conwell posted a message that read, in part: "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."

A native of Freeport, New York, Day was highly ranked and had won a number of matches over the years. He started as an amateur boxer before turning pro.