"It is with the deepest sadness that I tell everyone that early this morning, Jimmy Glenn, my father, passed away," his youngest son, Adam, wrote in an email on Thursday.
Jimmy Glenn was a longtime trainer, cut man and owned "Jimmy's Corner," a popular bar near Times Square, for 47 years.
Adam Glenn, the youngest of seven siblings, told ABC News he and his father were diagnosed with the coronavirus around the same time, but as the son recovered, his father's case, coupled with kidney disease, worsened every day.
"My dad is a vibrant 89-year-old who went to work five days a week," Adam Glenn, 39, told ABC News. "The fact that I had to pick him up and take care of him, to the point where he had no energy, I didn't feel it was safe to have him home."
Jimmy Glenn was admitted to NYU Langone Medical Center over two weeks ago, and his family learned on Wednesday that he was going to receive a convalescent plasma treatment after a litany of other medications weren't working.
"His condition rapidly worsened overnight, and finally his body just did not have the strength to continue fighting," Adam Glenn wrote.
Convalescent plasma contains special proteins that are produced in the blood of a fully recovered coronavirus patient.
"Convalescent plasma can also be used to manufacture a biological product called hyperimmune globulin, which can similarly be used to treat patients with COVID-19," the Food and Drug Administration said in a statement last month, encouraging plasma donations.
NYU announced a clinical study using the convalescent plasma on April 29 in which 300 patients 18 or older, who were hospitalized for at least three days but not already on a ventilator, could participate.
When Adam Glenn first announced that his father was diagnosed with COVID-19, he said there was an outpouring of support from in and around the boxing community, and later many people offered to donate.
"My dad has so many people that loved him," Adam Glenn said on Thursday, adding that once convalescent plasma became an option, he pushed his father's doctors to get him considered.
"Families are desperate right now, I know, but we don't know if its working or not. We don't have enough data, and it's very difficult to get data without a control group," said Dr. Corita R. Grudzen, who specializes in emergency medicine and is a researcher with NYU's clinical study.
Grudzen added that the available supply of convalescent plasma has increased over the last two weeks, saying that one person's donation can help more than one patient.
After the first week of the clinical trials, Grudzen said researchers have used the treatment on more COVID-19 patients.
"I'm heartbroken that I had to fight for this treatment, and my dad wasn't able to see if it worked for him. There just wasn't enough time left," Adam Glenn said. "Going forward, I hope families get to have this treatment and are able to bring their loved ones back home."
Jimmy Glenn was inducted into the New Jersey Boxing Hall of Fame in 2002. He leaves behind seven children, nine grandchildren and four great grandchildren.