Hi. My Son's Right Knee Was Somewhat Painful And Stiff

Hi. My son's right knee was somewhat painful and stiff this morning when he went to work. After 8 hours on his feet it is now swollen. Hurts to put weight on it. We have it elevated, ice on it and have taken ibuprofen. He does not recall injuring it. I was wondering if there might be some massage techniques to help circulate blood flow or mild exercises he could do when the swelling comes down?