Hello, Thanks for writing to us. 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, lipomas, cysts, growths from underlying connective tissue etc. Sometimes, a fluid filled structure just below the knee cap called infra 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. Wishing you good health... Regards. Dr Saurabh Gupta.