Keuchel had been DFA'd earlier this year by the White Sox and caught on with the Diamondbacks after being signed to a minor-league contract in early June, but was winless in four starts with a 9.64 ERA. He'll clear waivers and be a free agent again.
The 34-year-old Keuchel won the AL Cy Young Award with the Houston Astros in 2015 and is also a two-time All-Star and five-time Gold Glove winner.
When Keuchel was added to the Diamondbacks' 40-man roster, Arizona became responsible for only a prorated share of the $700,000 major league minimum, and the White Sox remained responsible for the rest of his $18 million salary this season. Chicago also owes a $1.5 million buyout of a 2023 option.
The Associated Press contributed to this report.