The former England captain's partner was diagnosed with cancer in December, which resulted in Strauss leaving the Ashes tour in Australia to fly home.
Now, Ruth is due to undergo a new course of treatment, which has led the former batsman to step down from his position on a temporary basis.
A statement from Strauss read: "We're very lucky that she's been very well until now. Although she is starting a new treatment on Friday that is going to be more challenging for her. As such, I'm going to be stepping back from my day-to-day duties while that treatment is going on."
Former England coach Andy Flower will replace Strauss for the time being.