Hi, thanks for writing to HCM. Well, I also agree with your trainer; this kind of symptoms generally relates to sprains/tears of tendon or ligaments due to strenuous exercises! There could be some loose bodies, synovial fluids or minor injury to patella, muscle or the tendons! I also suggest you to go for a X-ray / CT scan microbiological/cytological test of the secretion for confirmation and to relieve your concerns! Hope this answers your question. If you have additional questions or follow up questions then please do not hesitate in writing to us. I will be happy to answer your questions. Wishing you good health.