I have to admit, this is an issue related to preseason that I thought wasn’t important. Gustav Svensson is a more than serviceable centerback, so in a normal season that is adequate depth on an MLS team. It would only be a significant issue if both starting CBs were injured at the same time, which can happen (see early 2017), but isn’t something that a team should expend significant resources preparing for.
But readers here have me convinced that the fourth CB issue is something that needs to get sorted out. The World Cup starts June 14 and runs through July 15.