Clayton Richard will start Wednesday in place of Contreras.
Contreras is 0-5 with an ERA of 8.19 in six games.
"Good deal,'' [Richard] said when told he would start Wednesday. "Coming up last year and my whole career has been starting, I'm comfortable with that role. Any time you get an opportunity, you want to make the most of it and hopefully go out there and do what I'm capable of - but really just put the team in a position to win.''Last year, Richard, who is 25 years old, made eight starts. This year, Richard has an ERA of 4.41 in 11 relief appearances.
"His work ethic is second to none, and to see him struggling is tough,'' he said. "He'll figure it out. It's just a matter of time before he gets it clicking.''