Knee sprains (if that's what this is) are just freaking weird. They swell, they linger, and then all of a sudden they can improve very rapidly. It happened to me this summer, the doc examined everything, and said "Yup, it's a sprain. You didn't tear anything. You'll know when it's ready to go."
It didn't get much better at all for three weeks, and then it resolved almost completely in three days. Clay is a professional athlete with professional trainers. Until people start using the word "tear" or "damage" in association with "knee", I wouldn't lose my mind over this.