Kikuchi was selected to the American League All-Star team for the first time in his career and would have been Seattle's lone representative in Tuesday night's game at Coors Field.
The Mariners placed Kikuchi on the injured list on Sunday, but they did not disclose an injury, and manager Scott Servais said he could not comment but wasn't concerned about Kikuchi's status.
Kikuchi has been one of the top left-handers in baseball this season, his third since signing with the Mariners and moving to the major leagues from Japan. He is 6-4 with a 3.48 ERA and 98 strikeouts.
The Associated Press contributed to this report.