Considered the organization's top prospect coming into the season, Keller retired all five batters he faced in his eighth major league start. He is 1-3 with an 8.18 ERA.
Keller was struck flush on the outer part of the wrist. The Pirates said initial imaging revealed only a bruise.
"It still hurts but right away the worst comes to mind. That it's just a contusion and not broken is a relief,'' said Keller, who had his hand in a brace after the game. "Everything was working really good and I felt it was going to be one of those games that was going to be really good for me and the team. So, getting hurt is really frustrating.''
Clay Holmes relieved Keller.
The Associated Press contributed to this report.