Can impact to the knee cause a blood clot in a vein in the upper calf? the impact was not hard enough to any structural damage to the knee

Probably not: Trauma can cause injury to veins and or their flow. However the trauma would have to be significant enough to break a bone or do tissue damage. A minor impact would not likely cause a blood clot, but it is always a good idea to get it checked out by a doctor.

Injury and clot: An injury to a vein can cause damage to the vein wall and lead to a clot formation. However, for this to occur the injury would need to be significant and not minor trauma. The gold standard to evaluate a clot from the groin to lower calf would be a venous duplex ultrasound.