A 2 week old chick should not have symptoms of Mareks disease, a virus that can show up in chickens 3 weeks to 25 weeks and older. An injury or leg bone deformity might be a possibility. Slipped tendon can affect one leg and the hock joint might be red. Chicks can be defiencient in B2 or riboflavin. Get a chick vitamin with riboflavin—Poultry NutriDrench does not have it—or use human vitamin B complex 1/4 tablet daily crushed and sprinkled on food.
Pictures of the chick standing or being held up from the front or back might show if it is a leg bone deformity. Look for redness, swelling, or bruising of the leg or hock joint.