Restrict Scaling of Object due to camera position and angle.

Hi all, I am working in creating a ball game with unity. I used sphere as a ball. I have kept my camera at the center of the screen with some height. At center it looks like a ball but when i move ball on the left,right,top, bottom it look like oval shaped. I want it to be circle always. I have attached a sample images with ball at different positions for your reference. I hope someone can help me to solve this. Thanks in advance.