Qualls was on the 25-man roster for the Astros' wild-card game against the Yankees but did not pitch. The 36-year-old right-hander had a 4.38 ERA this season.
The only other noteworthy move made by manager A.J. Hinch was to include outfielder Preston Tucker, a left-handed bat who can handle the Royals' trio of right-handed starters. He replaced the more versatile Jonathan Villar, who would have given Houston an added element of speed.
The series begins Thursday night in Kansas City.