I asked FC Dallas today for an update on George John's injury (which appeared to perhaps be a groin strain?) and he's officially "Questionable."
I would take that to mean he won't play against Houston.
There are a couple of options to replace him. If Jair Benitez (he was Questionable earlier this week) is ready to go then Zach Loyd can play center back (or if Moises Hernandez is deemed ready). Brek Shea can play center back as well, but he's in such fine form at left mid I'd hate to see that.
Daniel Hernandez can play in the back as he did while playing for Mexican teams. Bobby Warshaw is also quite capable of playing center back as he did for two season at Stanford. After that things get a bit murkier and involve people like Jackson or Andrew Jacobson playing center back.
All of which underlines the need to sign a backup center back now that Kyle Davies has been let go. I think Schellas Hyndman knows that given the number of center back trialists we saw this spring.
So what do you expect to see against Houston?