Thanks for writing your query.
Persistent red streaks on skin after injury
can be due to cellulitis
as a result of injury.
Confirmed diagnosis can be made after clinical examination only.
You should get him examined medically and get his Complete Blood Count(CBC) done.
You can give him pain killer after discussing with his doctor. This will also help in reducing the swelling/inflammation.
will also help in relief of his symptoms.
Adequate rest to the injured part will speed up the healing.
I hope this is helpful to you.