Diaz is an extra coach who also throws batting practice during the season. However, he'll be on a bigger stage in New York.
"I'm very excited to go there," he said Saturday. "[I'll] just throw strikes, you know? I think for [Davis], throw strikes right where he likes it."
Showalter's not worried about how Diaz will fare, and said Diaz shouldn't be concerned if Davis doesn't do well.
"He'll be fine," Showalter said. "It's not pressure on something you do well. I don't see Chris as one of those types of guys that will blame anybody."
Jeff Seidel is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.