A 42-year-old woman from Mumbai undergoes elective femoral artery catheterization for coronary angiography. Three days post-procedure, she develops a tender, fluctuant swelling in the right groin with fever (38.5°C). Ultrasound shows a 4 cm fluid collection within the femoral triangle, separate from the artery. Blood cultures grow Staphylococcus aureus. Which structure within the femoral triangle is most likely to have been inadvertently punctured during the procedure, predisposing to abscess formation?