I'm not a vet, so this is not professional advice.
From the pictures, these look like seriously infected wounds that urgently need treatment, these will not heal on their own and likely get worse quickly if left untreated.
Apart from this obvious problem, the coat condition of this cat alone would warrant a vet checkup if you ask me.
As Stephie points out in the comments, the cat will likely need at least regular, uninterrupted medication (antibiotics, the treatment can make matters worse if interrupted!) over a period of time, which in itself is not very feasible for a stray.
Looking at the wounds, it will likely need to wear a cone for some time to give the wounds a chance to heal properly once treatment is started, again not feasible for a stray.
In my lay opinion, this cat needs to be caught and brought to a vet.
If the cat does not allow you to pick him up, the best course of action would be to contact a local TNR (trap-neuter-return) group, they usually have traps available they can lend you, and the experienced people to set them up properly as to not harm the cat in the process.