it is probably a bacteria infection, and will probably result in pop eye. He can get over it if it resulted from him bumping into something, just make sure that he is eating well, not getting bullied and isnt stressed from bad water quality.
If he got because he is stressed, you need to identify why he is stressed and take immediate action to fix that for best chance of recovery.
But if he does lose the eye, its not a death sentence. He might just only turn one direction.