Aaron Cook will undergo an MRI exam Monday on his strained right shoulder. He was placed on the disabled list Saturday with reliever Matt Herges brought up from Triple-A Colorado Springs to take Cook’s place on the roster. Cook is likely to miss a minimum of several weeks.

Since Cook was injured throwing a pitch to Nate Schierholtz in the fourth inning Friday and didn’t experience nagging soreness during his start against the Giants, manager Jim Tracy said he was told by Keith Dugger that is typically a good sign that the injury is not serious.

Tracy said a combination of Josh Fogg and Adam Eaton would likely be used Wednesday against the Dodgers when Cook’s turn in the rotation comes up. As to which one starts, Tracy said that would depend on matchups and history against the Dodgers players, matters Tracy will spend more time poring over in the coming days.

Assuming the MRI on Cook’s shoulder comes back clean and shows no structural damage, Tracy said the club might be looking at being without Cook for about three weeks, comparing Cook’s situation in that case to left-hander Franklin Morales when Morales was sidelined with a left shoulder strain earlier in the season.

Several weeks would appear to be the minimum time Cook will be lost to the team. In the case of Morales, he went on the disabled list April 22, one day after coming out of a start at Arizona, and wasn’t reinstated from the 15-day disabled list until June 12.

After next Wednesday against the Dodgers, Cook’s turn in the rotation comes up Sept. 1 against the Mets when the rosters can be expanded. Jhoulys Chacin might be a candidate to start for the Rockies in the final month, but his fastball command must improve.

That was Chacin’s downfall in a poor start Aug. 11 against the Pirates that resulted in his option to Colorado Springs. In his first start for the Sky Sox, Chacin threw 5 1/3 hitless innings Aug. 18 and was part of a four-pitcher tandem that threw a no-hitter. However, Chacin’s fastball command in that game at Oklahoma City wasn’t as sharp as it was when he was pitching at Double-A Tulsa before joining the Rockies or as sharp as it needs to be at the major-league level. Chacin is scheduled to start Sunday for the Sky Sox against Reno.

The addition of Herges, Tracy said, adds another long reliever to the mix, a variable that might come into play if Fogg or Eaton starts and gets knocked out early. In that case, Tracy would still be able to turn to Herges to pick up innings without having to use relievers such as Matt Daley, Rafael Betancourt and Morales earlier than usual.

In other news, shortstop Troy Tulowitzki is in the lineup. He didn’t make it to the ballpark Friday because of flu-like symptoms.

Yorvit Torrealba is starting at catcher, and Chris Iannetta will be in the lineup Sunday. Iannetta broke an 0-for-14 slide by lining a double to center on his final at-bat Friday. But with a day game Sunday after a night game, Tracy said he will start Iannetta on Sunday because he is 6-for-9 with two doubles, one home run and four RBI against Tim Lincecum, the Giants starter Sunday, and because Torrealba has worked well with Jorge De La Rosa, the starter Saturday.