Find something that interests Grigor. Does he like writing, drawing, movies, coloring, or sports? You have to find some way to connect to Grigor through trial and error. I had a silent student once and I made it a point to ask him a personal question every day. He wouldn't answer for the first few weeks or just nod or shake his head, but eventually he came around. Be persistent in your attempts to reach out to him, and do not give up. If you find something you can relate to him with, he may come around. Ask his parents what he enjoys doing and somehow relate it into the content learned and allow him to use his talents in class.