Volquez, who could be the Opening Day starter, has hit the dead-arm stage of Spring Training.
"His arm is heavy, a little fatigue," Yost said. "We're going to back him off one start, just have a side session."
Right-hander Dillon Gee, just added to the 40-man roster, will make the start on Friday in San Antonio. Chien-Ming Wang, one of the surprises of camp, will get the start on Saturday.
Meanwhile, in the split-squad games in Surprise, right-hander Miguel Almonte will start on Friday and Matt Strahm on Saturday.
Mr. Black Belt
Yost shared a story on Wednesday about how he almost got his black belt in Taekwondo.
"Started taking lessons in 1980," he said. "And I just kept advancing -- boom, boom, boom -- all the way to the point of taking the black belt test for Taekwondo. But that was in 1982 and I wanted to wait until after the World Series.
"But after we lost the World Series, I was bummed out and never took it."
What inspired Yost to try Taekwondo?
"I got into it for the flexibility," he said, " ... and I like to fight."
Dyson throwing Jarrod Dyson, who was expected to be the Opening Day starter in right field, continues to rehab from a Grade 2 oblique strain.
Dyson began throwing short tosses on a side field on Wednesday and reported the discomfort is lessening.
Jeffrey Flanagan is a reporter for MLB.com. Follow him on Twitter at @FlannyMLB. This story was not subject to the approval of Major League Baseball or its clubs.