This is most certainly a case where easing into it is preferred.
The subject of a loss can be very touchy for some, whether or not it is the reason they were away from work. I can personally testify to this as when dealing with a loss myself, sudden queries from sympathetic friends would sting more often than they would comfort.
If you have a somewhat regular method of contacting them, then reaching out the usual way would help and even then avoid explicitly mentioning the suspected bereavement until you have had some more subtle build up to "test the waters". For example:
We missed you at work today.. [wait for response]
and if they don't mention why they were absent but showed no signs of distress then a further prompt could be okay:
Is everything okay?
However, if you would not normally contact them outside of work then it is probably best to wait until you hear from him. Going out of your way to press this particular topic onto someone stands out and often may only upset them. If your suspicions are correct then you would not want to push the matter with them personally, perhaps asking third parties could provide you with the answer you need and if he is fine then I'm sure he will soon let you all know.