Z is not a traditional big man and playing him at the five will not work until he gets serious about building his body. He is a good passer, a decent shooter, and has a good sense of timing. He will get punked by any center that has athleticism or mass.
After watching his brother I have to wonder if Z wasn't playing the 4 while his brother played the 5 during their childhood. He has zero idea how to block out or how to hold his position. His screen setting skills aren't great either.
Maybe that's why he came stateside, to learn how to play down low. If so Cal is the last person on earth he should be attached to.