Noticed A Knot In The Leg And Swelling Of Ankle

Reading the below knot on leg, my husband one week ago came home from running. He is a marathon runner and has had numerous injuries, but runs through them all as he is on the National Streaker Registry. A day later he noticed the inside of his ankle was swollen, then in several days, swelling went down, but bluish red in color and on the inside calf appeared a large knot and his leg hurts. At first look, I thought he stretched or tore a ligament. He said a running friend suggested a blood clot. I put a heating pad on his knot with a damp cloth between, to keep warmth longer, 20 on 20 off. What is your opinion. I told him he needs to get it checked, because he could be making it worse by his daily constant running. He averages 3-6 miles a day. Thank you and God bless