Chen was making his first start since May 5, after three minor league outings in which he went 0-1 with an 8.18 ERA. Chen was 4-1 with a 3.59 ERA in seven starts for Kansas City before he was hurt.
The Royals optioned left-hander Everett Teaford to Triple-A Omaha to make roster space for Chen. Teaford had a 2.84 ERA and no decisions in 14 relief appearances.
With Teaford's demotion, the Royals are going with a seven-man bullpen and 12-man pitching staff.