Ask HN: How to respond to an employee that has psychological problems

Our startup is doing quite well, and we have a small team of engineers. We have one UI/UX Designer in the team on whom we heavily depend on. He is a good designer. Over the last two months he has been very irregular to office, and barely getting anything done at all. I pulled him aside for a performance evaluation conversation today, and he broke down and told me that he has serious psychological problems, and has been seeking professional help. I want to support him as much as I can, but we are bootstrapped startup, and I cannot afford to hire another designer to fill in for him, while he is on recovery. What would you do in situation like this?. I really want to keep him onboard, but he is very expensive for us to bite the bullet easily.