Contreras, who has pitched in the postseason with the Yankees and the White Sox, struggled to 5-13 with a 5.42 ERA in 21 starts with the White Sox this year. Contreras has been healthy this year, unlike in the past when he battled leg injuries, but admitted his mechanics have not been good.
To be effective, he'll have to command his fastball and rediscover his split-finger pitch, which he uses for strikes and to entice batters to chase. Contreras said he thought a bullpen session on Wednesday with Rockies pitching coach Bob Apodaca was productive.
"This is the first year I've felt healthy," Contreras said. "In previous years, I've had different issues with my legs and my body. It is mechanics [that have created issues].
"I feel like I was thinking too much in Chicago. The change of scenery and starting here with this team, I feel, will relax me."
Rockies catcher Paul Phillips, who faced Contreras when he played for the Royals and caught him while with the White Sox, said Contreras brings raw talent and a pleasant persona to the Rockies.
"I remember when I was with Kansas City, and when we faced him we were like, 'We've got Contreras today ... super ... It stinks,'" Phillips said. "Last year, to be there with him and catch him was super. Even though he's a veteran guy, he still likes to listen and try to learn. He's a quiet guy, but you should listen when he talks because it's probably going to have some meaning behind it."
Manager Jim Tracy said he is eager to see what Contreras provides.
"If he can get to the point where he can get to the strike zone, he's not an easy guy to hit," Tracy said. "If he throws his fastball for strikes and it gets him to the point where he's able to throw his split and get his split near home plate, he's going to get swings, bad swings, from the opposition."