Hairline fracture on tibia?

[NyMe18]

Does anyone know anything about hairline fractures on the tibia?
My 5yo has been very whiny this afternoon, wanting to be carried and complained about pain in his leg. We just thought it was growth pain/him not waning to walk though that’s not common for him to do.
He fell asleep for the night and woke up at 12:30 am in pain crying. Squirming and whimpering, complaining about his leg. That’s when I discovered the bruise he has, it’s perhaps a bit over an inch in diameter and it’s raised and hard. He’s slightly swollen around it as well. He won’t tell me what happened more than that he fell. He finally agreed on some pain relief which he doesn’t do easily as he absolutely hates it. Now he’s calmed down and is able to lay still and relax. If the acetaminophen worked is it safe to say that it’s just a very nasty bruise? How can I tell if it’s something like a hairline fracture and worth going to the doctor? I’d feel so silly dragging him to the ER over a bruise..