Not knowing anything more than a vague “abdominal” injury, and please
@Doctor Hoop chime in; I believe most injuries to the area are a result of a twisting movement that strains the abdominal complex. What’s especially complex about the abdominal muscles is that relatively few attach to bone compared to limb and back musculature; rather, fascia. And, the core/abdominal muscles can’t be rested/immobilized much, as they are so key for every normal movement we make in day to day life. So an injury to a small oblique muscle can linger for a while.