"He's our No. 1 starter. It was an easy decision," manager Ned Yost said of Duffy. "And he's healthy."
Right-hander Jason Hammel will start Friday and right-hander Ian Kennedy will be on the mound on Saturday, setting up Duffy to match up with the Dodgers' Clayton Kershaw in the final game before the All-Star break.
Duffy (5-4, 3.51 ERA) returned from the disabled list on Tuesday, after being out since May 28 with a right oblique strain. The lefty settled in after surrendering a pair of first-inning runs, allowing just those two runs on five hits over 5 2/3 innings in a win.
Wood (1-2, 6.06) has pitched in 26 games this season, but has made just one start, in which he allowed two runs over four innings against the Twins this past Sunday.
Josh Horton is a reporter for MLB.com based in Seattle and covered the Royals on Wednesday.