Reading between the lines, I think it is going to be Jerebko. They need to replace Amir, and the choices are Zeller, small lineup of death, or Jerebko. My guess is that he picks the middle option in order to try to increase defensive intensity without giving up too much size.
I'm okay with that, but if Lopez starts to board Horford, he needs to go to Zeller to put a body on him.