Sounds like the quail may have been pacing against something to get that wound?
Even the quail in my planted aviary pace sometimes because they want to get to the brush on the other side of the hardware cloth causing beak scrapes but usually no blood unless there's a problem like they're being chased so they really push when they pace.
In the aviary, the injured bird can hide so it's not a big deal but as you can see they love pecking at wounds :O
I would keep the bird in sight like right beside the cage or even inside of it in a smaller cage if possible so that when it's healed you can just put it back in with probably no problems.
If it's bleeding, you can put some corn starch on it - stops bleeding for a lot of wounds like nail/beak injuries and on cat and dog nails too if you clip them too short