Okay does he really want to work with you guys? hows his economy otherwise? what DOES he want from life?
Do my old boss did when I acted like this, ask me if I need time of, witch I took and never came back to that place I think right now he's done, he sees no future and mopes about life. I know it I've been there, and I get back there from time to time. Everytime it happens I have to remind myself "Okay, I've been here before i know what to do to get out of here" . This time it means quitting my job and travelling to Thailand to become an English teacher and train Thaiboxing there for a while.
I have no idea what his situation is like, but as a fellow ENTP i would try to find what he wants and talk to him in Ne language With Ti, and Fe as backup to find the solution. Ask questions, make a mental map of what he seems to want with Ti ues Ne to find ideas, entertain his ideas with more Ne. My Intp friends can be great at doing this (if they are interested in what im talking about otherwise my Fe tells me they find me a drag, and i switch subject)
<B>Core of it all, Find out his fututure</B>
Ps. He might be seriously depressed or mentaly ill, you need to consider professional help although every ENTP would be very reluctant to that .Ds