Any Cubs fan knows that even with their team resting comfortably in first place and on the brink of capturing a postseason berth, you just can’t take anything for granted. Case in point, the front of the Cubs’ starting rotation is experiencing some arm troubles.

Carlos ZambranoCarlos Zambrano will undergo an MRI to determine the severity of his arm injury after leaving Tuesday nights start with a sore shoulder. Even though he says the situation isn’t serious, Rich Harden also admitted to having some arm “discomfort” and will skip his next start as a precaution.

Regardless of the severity of Harden’s condition or the contradictions built up the last few days, the timing of the media circus building over the pitching staff couldn’t be worse for the Cubs, coming on the heels of Carlos Zambrano leaving Tuesday night’s start with a sore shoulder.

With the balance of Zambrano’s season hanging on the outcome of today’s MRI exam, the double dose of soreness at the top of the rotation raises the scrutiny as high as the stakes in Harden’s next start, which should come Wednesday in St. Louis.

”Look, if he were available to pitch today, or tomorrow, or the next day, why would we wait for St. Louis?” Piniella said when pressed on the reason for Harden being given 11 days between starts. ”Doesn’t that make sense? He’s not available right now is all I’m trying to tell you. And he’s going to be available for the St. Louis series.”

Pressed again, Piniella revealed the ”discomfort.”

Everything is serious when it comes to Harden because he has a history of not being able to stay healthy. “Discomfort” might turn into something more and if Zambrano has to be shut down for an extended period of time, the Cubs can’t afford to have Harden sidelined. Worse case scenario, if both Zambrano and Harden were seriously injured, the Cubs would have Ryan Dempster, Ted Lilly, Jason Marquis and Rich Hill/Sean Marshall as their postseason rotation. Yikes.