If he's that wary of strangers, doubtful that a rescue would take him in, because they're mission is to adopt out pets, usually. Although some adopt out feral "barn cats" if you're in a rural area. Better to take him to an agency that does Trap-N-Release (TNR), where they spay/neuter, give shots, and tip the ear, then you let him back into his colony.
I would put out a live trap or a dog crate with tuna fish or canned chicken and see if you can trap him. Then take him to a vet to get treated and checked over for injuries.
Hopefully he felt well enough to come to you to get help, and hasn't gone into hiding to die, poor baby. My mom's indoor/outdoor cat disappeared for 3 days and then showed up out of nowhere with a nasty wound. I think their first instinct is to hide, lick their wounds, and try to heal up and gather their strength in case they get attacked again. Then go look for help.