The front of the Boston Red Sox's rotation looks something like this: Jon Lester, Josh Beckett, and Clay Buchholz. Solid. Then there's this escarpment, and on the ground below, there's a big competition for the final two spots. Carlos Silva already had to drop out. Now it looks like Aaron Cook is out, too, at least for the time being. Nick Cafardo:

[Bobby Valentine] On Aaron Cook: "Will he get enough innings to start in the major leagues at the beginning of the season? I doubt it. Seems he's like he's on a pace for 17-18 innings if all goes well. If we have the innings to give him, maybe, but I doubt it."

Cook's got himself an injury history, hence the kid gloves. Valentine hasn't shut the door on Cook making the rotation eventually, but it's not going to happen out of the gate.

Fortunately for the Red Sox, while Cook is out, Andrew Miller is back in. From the same article:

Valentine thought Andrew Miller's situation was different from Cook's because Cook is more of a rehab situation, while [Miller] has missed time with a sore elbow. Valentine reported that Miller threw a bullpen and appears to be on the track back and still able to compete for the No. 5 job.

So the battle rages on. Two guys will win starting jobs out of camp, presuming the Red Sox don't suddenly sign Roy Oswalt somehow. Of course, the fight doesn't end there - the two guys will then have to hang on to their jobs, which is a challenge. The season is long. Winning a spot in the rotation is not the same as keeping a spot in the rotation.