Whenever the Colorado Rockies take the field, it’s prudent to check who’ll be on the mound. When Ubaldo Jimenez pitches, you know the Rockies have a good chance of winning. But if another pitcher is slated, it’s not such a sure bet.

Aaron Cook, the Rockies’ one-time opening-day starter and the team’s winningest pitcher, may be Colorado’s biggest liability as a starting pitcher right now. Cook was shelled last night at Target Field in Minnesota, giving up five runs in the fourth inning and heading to the showers early.

MLB.com reports that Cook (pictured) is now 0-4 on the road, with an ugly 7.38 ERA. He’s given up 56 hits and 22 walks. Perhaps it’s time to start thinking about baseball in Colorado without him.

“How exactly do I need to be out there?” Cook tells MLB. “Do I need to make a perfect pitch every time? Well, maybe next time, I’ll try to make a perfect pitch every time. But for me, if I’m pitching to contact and getting ground balls that aren’t hit hard, that’s all I do.”

Meanwhile, the Rockies’ offense is showing signs of improvement. Shortstop Troy Tulowitzki, coming off some downtime for a strained groin, hit his ninth home run of the year, and outfielder Carlos Gonzalez earned his team-leading 42nd RBI. Todd Helton, who has spent much of the year in a discouraging slump, has also played better of late, claiming his second home run of the year.

Another bit of good news: Closer Huston Street is on “the verge of returning,” writes The Denver Post, which would bolster a bullpen that’s on pace to be the best group of relievers in team history.