"How eager is Aaron Cook to get back in the pennant race?

"I told (manager) Jim Tracy the other day to just give me 20 minutes notice and I'll be ready," Cook said.

Tuesday afternoon, Tracy informed the right-hander he would start Friday night's game against the Cardinals. Cook will be limited to about 70 pitches, but at least he's in the mix to pitch in the postseason, if the Rockies get there.

"I don't care how many pitches I get Friday," Cook said. "I just want to go out there and do what I can."

Tracy chose Cook over veteran righthander Jose Contreras. Contreras' strained right quadriceps appears to be healed, but Tracy isn't ready to chance Contreras having to make a quick play in the infield.

Cook, the Rockies' opening-day starter, was 10-6 with a 4.47 ERA when he felt pain in his shoulder Aug. 21 in the fourth inning against San Francisco.

Cook used his rehab start to work on a changeup, a pitch that could complement his sinker and four-seam fastball.

"It's not a pitch I'm going to rely on but if I need it and there's a good situation, I'll probably throw it," he said."