Is your character about to have his first fight ever? Is he trained in fighting? If not, then there are some injuries you might want to consider….
Often in novels there is a side-kick to the main character who is perhaps a bit book smart, but not a fighter. So, when that side-kick is confronted by someone who did or said something bad, everyone is surprised when said character punches that person in the face.
She has never punched anything before, yet somehow manages to knock that evil person out cold while sustaining no injures to herself.
In reality, punching is not as easy as making a fist and smacking someone with it; hold your wrist wrong and you might break it. Hit with fingers rather than knuckles, and you might break those too. Hit correctly, and you might still get broken and bleeding knuckles.
The truth of the matter is that a common injury to professional fighters is a broken wrist from punching wrong. If they can make a mistake and get injured, what about your character? The human face is surprisingly hard; so hit it for the first time, and you might feel like you just punched a brick wall.
To make your novel seem realistic, perhaps consider at least having your character shake out their sore hand…because “sore” is something it certainly would be.