Red and warm knee cap. Dont recall hitting it?

Bursitis. The pre-patellar bursa can sometimes become inflamed by repetitive kneeling or bumping the knee. Though this bursitis usually resolves with anti-inflammatory meds and avoidance of kneeling, sometimes the bursa becomes infected as well which requires antibiotics for treatment. Your primary care physician or orthopaedic surgeon can help with the correct diagnosis.