Your description seems to suggest a discreet swelling. As you have not mentioned the exact location of the swelling, let me list some of the possibilities.
- an organized clot (bleeding from a partially torn muscle). Initially painful, but persists after the pain is gone.
- a muscle hernia (this happens when the deep fascia overlying a muscle gets torn and the muscle protrudes through the defect)
- a soft tissue tumor.
You should consult a doctor and obtain an opinion & refrain from ignoring it just because it is painless.
MB BS, MS, FRCS(Edinburgh)