He sees it on the front of his jersey every day. And it reminds him just how fortunate he is to be playing the game he loves at the highest level possible.
Five days before the 2014 draft, Jefferson found out that his former Baylor teammate and close friend, Isaiah Austin, would not be joining him in the NBA.
Austin had been diagnosed with Marfan syndrome -- a genetic disorder that affects the body’s connective tissue. His NBA dream, which he had come so close to fulfilling, was over.
“When he got the news, it definitely hurt him,” Jefferson said. “I remember when he told me that he couldn’t play. It was a Saturday night, five days before the draft. He told me he wasn’t going to play anymore, and I went right over to see him.
“We just talked -- talked about everything -- but he’s definitely turned it into a positive thing, gotten his story out and helped people however he can.”
Since his diagnosis, Austin has become an inspirational speaker, taking his words of wisdom across the country.
“I think I’m coping with it pretty well,” Austin said. “It’s just something that I have to deal with, and it’s been a new beginning for me. I’ve met a lot of families and children affected by Marfan’s syndrome. These kids are warriors, and their strength inspires me.”
Austin’s strength inspired Jefferson. After speaking with him that night, Jefferson decided that he was going to wear No. 21.
“I didn’t tell him,” said Jefferson, who wore No. 34 in college. “I just did it. He liked it, just being able to see No. 21 still out there. Like I said, it means a lot more to me now.”
Wednesday night, the Celtics honored Austin for his courage and presented him with a framed No. 21 jersey.
Later, Jefferson -- this year’s “Mr. Irrelevant,” who made the Nets out of training camp -- scored eight points in his NBA debut.
Fittingly, Austin was in attendance to see it.
“[Cory’s] a guy that’s really worked to get where he is, and I’m really happy for him,” Austin said. “Because he really deserves it.”
The two were able to go out to dinner and catch up Tuesday night.
Their friendship remains strong -- connected now and forever by the No. 21.
“I’m still getting over it,” Austin said. “I still miss the game every day of my life. At the same time, I know I have a different path that I’m taking and journey that I’m on right now. I’m not dwelling on it. I’m moving forward and I’m staying positive.”