Thank you for the question. May I ask what type of injury? That would lead me in the right direction to answe. is there voicing? How is his comprehensio? respiratory status? Looking forward to your response.

First, like Mrs. Mayya, it would be helpful to know what type of injury he suffers from. Secondly, assuming his vocal chords are fully healthy, the only other possible physical disablement that may be causing him to not speak would be his breathing and lung capacity. However, if that's alsi fully functional and his lack of speech is purely voluntary, an unwillingness, then there's only two things I could suggest. (1) The first, less aggressive, approach would be to simply play some music he likes and sit in the room with him and start singing along. This would encourage him to start singing as well, and that would work as a way to get him to restart using his vocal chords, but without any obligation. That is,  just by singing along, his words don't have any "consequences", so he shouldn't be afraid to say them. (2) The alternative, less pleasant and more aggressive approach would be to give him two options, but he needs to speak to tell you which he chooses. Along the same lines as the music choice, that could be as simple as telling you which band/CD he would like for you to put on. And don't hold up the CDs, but just lost the options and ask him which he'd like best. Then, instead of just pointing at his choice, he would actually need to speak and tell you his choice! Worst case scenario he still refuses to talk, you might need to use some more aggressive mean. For example, the two music choices are one band he really likes, and one he really hates. If he refuses to talk, then put in the one he dislikes, and let him kno that he can simply tell you to switch, but only by using his voice. Of course, you should only use this option after trying the other ones, and even then, only once all physical inability reasons have been definitively ruled out.  Hope this helps, and best of luck Moniquebtown!