Hi and welcome to HCM Well, without a clinical evaluation it would be difficult to determine the cause of the lump. Possibilities that may need to be considered include enlarged bursa, cysts, growths from underlying connective tissue etc. Sometimes, a fluid filled structure just below the knee cap called supra patellar bursa is chronically inflamed, with or without pain, due to some infection or trauma and the process causes fibrosis and inflammation, making a lump like structure below the knee cap. I would suggest getting this evaluated by an orthopedician for an accurate diagnosis and appropriate management. You may get the X-ray of the area affected and FNAC (fine needle aspiration cytology) of lump under his/her guidance. Hope this will helps you. Take care.