Non-recruited, non-preferred walk ons face two huge hurdles:
1. Being good enough to play after not being good enough to be recruited. Most walk-ons don't clear this hurdle, but your friend might because he looked recruitable until he got hurt.
2. Getting enough of an opportunity to demonstrate his talent at an open tryout. I watched the open tryout at my son's school freshman year after the team scrimmage on the first official day of fall practice in late September after the scholarship athletes and preferred walk-ons had been working and working out together since the beginning of summer school in July. The tryout was a perfunctory formality: the players didn't get to hit, so it would have taken eye-popping velocity or foot speed to get noticed in the half hour or so they took to eliminate the entire group of two dozen aspiring ball players.
Your friend needs a strategy to overcome the second hurdle by making sure the coach knows who he is before the tryout. Because he is a catcher, willingness to be a bullpen catcher could be part of the strategy. Because at one point he was recognized as having D1 potential, asking travel, high school, or college coaches who saw him before he was hurt to attest to his ability could also be part of the strategy.
Best wishes,
P.S. I just realized I said what BOF said, but in more words.