I work in academic environment and one of my students has an anxiety disorder.  The student is in my mind a very promising young scientist but I have the impression that his mental health problems are getting the better of him and I would really like him to feel more at ease to reach his full potential but I   don't really know how to properly support him.

The field I am working in is quite competitive and to reach a high standard, people have to learn a lot in short amount of time. The work is challenging and I kind of depend on my students to tell me, when they need more assistence. However, this student is obviously very afraid to admit mistakes, which leads to him trying to build a wall around himself instead of asking for help when he needs it. I tried to tell him that it is ok, if there is something he doesn't know and that he should communicate problems he is experiencing, but he doesn't. He seems to be overthinking things a lot and tries to solve all problems on his own and hide it if he can't. In this manner, he is wasting a lot of time and seems to be overwhelmed by the workload. I am pretty certain he has the ability to keep up, but the anxiety is getting in his way. He has a lot of trouble with the public presentation of his work, spending weekends in the office, trying to make a perfect presentation but then stumbling trough it because he is so uncertain of himself. I got him to open up little in the past months and while we working together very closely it got better but now I switched to a different department and can not supervise him as closely. 

I tried to talk openly with him and told him that he needs to communicate about what is going on but he has stopped to do so and I feel that this will lead to more mistakes and then more anxiety about the mistakes and more hiding away. So my question would be, how do I break this downward spiral? How can I instill more confidence in him? Those of you, who have experienced these kind of situations, how could a teacher build the trust that is necessary for a constructive learning environment?