Remember, the 39-year-old former defensive lineman revealed back in July 2019 his kidneys had failed ... and he was in dire need of a lifesaving transplant.

Nearly 2 years later, Haynesworth found his match -- a physical therapist assistant from Arkansas named Zach Penny -- and underwent successful surgery in April to receive the new kidney!!

Haynesworth recently spoke about his recovery with Paul Kuharsky ... saying, "Now, I feel better,"

"I see changes in my body. Now I am kind of discovering another new norm."

Haynesworth added he believes his kidney failure stemmed from taking anti-inflammatory shots before every game of his 10-year career.

"At 33, 2 years out of the league, my kidney function was below 50 percent," Haynesworth said. "So it has to be the junk that we were taking, like Toradol. Everybody used to line up to get their Toradol shots and take the pills afterward and all of that s***."

"I guarantee that had a lot to do with it because that really kills the kidneys."

As for Penny's willingness to help out and donate his kidney, Haynesworth calls him a "real living angel."

"This kind hearted selfless human being drove seven hours from Arkansas to give me one of his kidneys!" Haynesworth said on Instagram. "This is one of the happiest days of my life next to the birth of my kids."