Hi i am Dr Ahmed Aly thanks for using healthcaremagic site , I had gone through your question and understand your concerns .. In my opinion if it is a contusion it will resolve with the foments ,ibuprofen , physiotherapy , massaging with a topical gel containing muscle relaxants ,anti edematous drugs for the swelling , arm sling , elevation of the hand would help if the lump didnt resolve within 10 days i recommend MRI for proper evaluation and management which if showed a complete tear to the muscle . .which may need endoscopic or minor surgical intervention, which i think in your case wouldnt need such interventions . Please click THANK YOU and consider a 5 star rating with some positive feedback if the information was helpful. Hope the above information helps you, Any further clarifications feel free to ask.