"He's a guy we're working [with] on with some things," Hurdle said. "He is a sinkerball pitcher, and he needs to re-affirm the fact and conviction of sinking that ball and repeating that delivery.
"We want him to have a slider in his back pocket, but we don't need him to be a two-pitch pitcher right now. We have to help him back to being a power-sinker guy that he's been since he's been here."
Meanwhile, Mazzaro has yet to allow a run this year in seven innings over three appearances with Triple-A Indianapolis and four innings with the Pirates.
"We've liked what we seen," Hurdle said. "The fastball is firm with some late sink. [He's] come in and thrown strikes and been aggressive in the zone. Left-handers haven't barreled him up yet."
Michael Radano is a contributor to MLB.com This story was not subject to the approval of Major League Baseball or its clubs.