Bad news for Rockies fans coming out of Colorado. Ace Aaron Cook has been placed on the DL due to shoulder strain. The team has called up right-handed reliever Matt Herges from Triple-A Colorado Springs to replace the injured Cook on the roster.

The Rockies began the day leading the NL wild-card race by one game over San Francisco.

Cook was hurt during Friday night’s 6-3 loss to the Giants. Rockies manager Jim Tracy said Cook felt something in his shoulder during a four-pitch walk to Nate Schierholtz to start the fourth inning. Cook motioned to the dugout after the walk and was taken out after being looked at by trainer Keith Dugger.

Tracy said Cook will have an MRI on Monday and the early signs are encouraging that it won’t be a serious injury.

Cook hasn’t been on the DL since 2007 when he experienced an oblique strain. With that injury, Cook missed the last seven weeks of the regular season. There’s word that Cook could miss up to three and a half weeks with this recent problem.

With a rotation of Cook, Ubaldo Jimenez, Jason Marquis, Jason Hammell, and Jorge De La Rosa, it’s a miracle the Rockies are in the playoff hunt. Normally, I would say that Cook’s absence wouldn’t hurt their chances — as he’s usually pretty mediocre — but he’s been vital to the Rockies unexpected success. On the Rockies DL, Cook will be joining relievers Manuel Corpas and Juan Rincon.

Still, the Rockies aren’t the only club in the NL West having to soldier through pitching injuries. All on the DL, Randy Johnson of the Giants and both Hiroki Kuroda and Jason Schmidt of the Dodgers can only watch as their teams compete down the stretch.

Either Adam Eaton or Josh Fogg will start in place of Cook next Wednesday against the Dodgers.