Need advice for implementing a friend with a medical condition who wants to play, but cant be on as much as everyone else.

Hello!

I could use some advice. I am about to begin a campaign with a group, and one of our close friends wants to join. Unfortunately this friend has a medical condition and for various reasons, he would not be reliable to be on when the entire party is on. Sometimes he might be on the whole sessions, other sessions he could be on from 80% of the session to 30% of the sesssion. Other times he might not be on at all. If this were your Campaign you were DMing (standard fantasy trope). Would you have him make a character just as everyone else and have him as a "ghost" following aorund the party when he has to go or isnt there. Would it be a divine diety with normal powers, or someone that comes to help when you "summon him". Any thoughts or ideas would be appreciated.

Want to add that we all WANT him to play, its not a question of saying no. its a question of what would be the best way of making sure everyone has a good time with the situation. Multiple ideas would be welcome so that we can give him options if they make sense.

Thanks so much!!