Knees are not something you need to rush out and hit with a MRI within a short period of time. I am sure they controlled the pain and swelling on the trip and since they would not have got back till Christmas eve day they probably did one on Saturday or are doing one the beginning of this week and then deciding on treatment options this week. With the way he was walking on the floor on Wednesday it is not good for the short term for sure. He was walking without crutches but it wasn't pretty.