Wounds are a part of a fighter's characteristic profile, like weapon skill and movement.
Weapon attacks and falling and such can cause WOUNDS, which are subtracted from the number of Wounds on the fighter's characteristics profile. Each time damage brings that number to zero or below, the number stops at zero, and an Injury Roll is made, which can cause a FLESH WOUND, which is entirely distinct. The next time damage is caused to the fighter's Wounds, which would again bring it to zero or below, it again stops at zero, and another Injury Roll is made. But a Wounds characteristic of, say, 3, means that the fighter needs to suffer 3 (or more) "wounds" worth of damage from hits before the first Injury Roll is made.
A Flesh Wound resulting from the Injury Roll does not in itself cause additional Wounds damage.