In discord, can I maintain a conversation with only one player while listening to the whole group?
Solution 1:
This is called whisper functionality, which Discord currently doesn't feature. Here you can vote to have this implemented.
Currently, you have to use one of the following workarounds:
1) Use a voice chat, which has whisper functionality, e.g. teamspeak.
2) Send the player the private message via text. This is cumbersome, but I feel the best solution, if you want to continue using Discord.
3) Call the player via discord. This removes you from the group chat for the duration of the call.
4) Move the player and you to a secondary audio channel. Also removes you from the group chat and makes it obvious you are relaying a private message to them.
5) Create a second discord account and use that to relay private messages to your players either via option 3 and 4. This allows you to stay in the main channel, but requires mic on/off juggling, whenever you want to send a private message (mute your main account while sending the message, then unmute after having finished)