The Oakland Athletics are going through a controlled purge as they overhaul their roster for the 2015 season. The four players who have been traded all shared All-Star status, but more importantly they fell into one of two categories:

1. Close to free agency (Samardzija)

2. More likely to get worse next year than better (Donaldson, Moss, Norris)

Watching those familiar names leave town makes you wonder who else from the 2012-14 core might be on the block. Josh Reddick and Sean Doolittle are both at risk, but there are reasons to believe that each of them could stick around -- Reddick could still have some improvement left in him with a healthy wrist, and Doo is signed for an insanely cheap salary. Sonny should be safe for another year or two. Eric Sogard probably doesn't have a lot of trade value, and Coco's not going anywhere. John Jaso is a candidate, as a 31-year-old who can be a free agent at the end of the season, but he probably needs to re-prove his health before he's a viable trade asset.

That leaves us with one more obvious name: relief pitcher Ryan Cook. The right-hander fits the bill. He's entering his first year of arbitration, and by AN's estimate he should make about $1.3 million next year -- that number will rise quickly in subsequent years. He'll turn 28 next summer, and it seems unlikely that he'll ever pitch better than he did in '12 and '13. And the A's already have his obvious replacement in R.J. Alvarez, acquired in the Derek Norris trade.

Evaluating Cook

Cook established himself as a top set-up man in his first two years in Oakland. In 2012-13, he posted a combined ERA of 2.30 with more than a strikeout per inning. His All-Star selection in '12 was a bit of a stretch, but he was clearly a top weapon. He stumbled a bit due to injuries in 2014, but he still ended up having a good year and he kept the strikeouts coming. For a team looking for relief help, he would seem to be quite a prize.

I'm not as excited about Cook, though. For starters, he's gotten worse each year he's been in Oakland. After bursting onto the scene and riding a low hit rate to a quick All-Star berth, he saw that hit rate rise up to more normal levels in 2013 while his strikeouts also went down. In 2014, the hits went back down, but he started walking more batters. It's not that he's necessarily going to be a bad pitcher from now on, it's just that we might have already seen his best season in 2012. He put together personal best-case scenarios in K rate, walk rate, hit rate, and home run rate, and he's unlikely to enjoy that perfect storm again. He can probably piece together two or three of those strengths in a given year, but that just means that it's time to sell him now while he's an eighth-inning set-up guy instead of next winter when he might just be a seventh-inning middleman.

It's not that I don't think Cook is good, it's just that I think he's replaceable and that the time to strike is now before his health goes south.

Cook's health is another angle to this, and it's not something I have a lot of confidence in. He missed all of spring training in 2014 with shoulder inflammation, and then he missed nearly a month in the first half with a forearm strain. It's one thing to have a history with your shoulder or your elbow, but to have problems with both in the same season is a big red flag to me. I was sure the forearm strain was going to lead to Tommy John surgery, but rest turned out to be enough ... for now. I still think he's a ticking time bomb who could go down for a whole season at any moment, whether due to an eventual TJS or due to his shoulder flaring up again. Sure, you could say these things about any pitcher, but Cook's recent history gives me cause to specifically worry about him. He has three years of team control left, so if you lose one of them to a major operation and then another half of one to his recovery, then you'll wish you'd cashed in on him via trade back when he was healthy and valuable.

And then, there's the more silly subjective part. Cook has entered into 84 save situations, whether in the ninth looking for a save or in an earlier inning looking for a hold. He's blown 16 of those chances, for an 81% success rate. That's not particularly good or bad, it's just kind of "meh." It's something that I think another solid reliever could do for less money, freeing up Cook to be traded for value elsewhere. In other words, there is no marginal value to keeping Cook over a newbie like Alvarez or Chris Bassitt, who could reasonably match his production, so to keep him would be to waste the potential value of trading him.

To make matters worse, his postseason record is atrocious. I don't put a lot of stock into postseason stats, but in the case of a relief pitcher it might tell us something about how well that hurler endures a long season with something left in his arm for October. In his postseason debut in Game 2 of the 2012 ALDS, he blew a lead by uncorking a game-tying wild pitch -- ruh-roh. He was good in Games 3 and 4. Then in Game 5, he entered in a 2-0 contest with two runners on and one out. He allowed a single, a walk, and a HBP to score both inherited runners, and by the time the inning ended it was 6-0 Tigers. In Game 4 in 2013, he faced four batters, allowed a single and a walk, and then saw both runners score after he'd been pulled. So, he's pitched in five postseason games and sucked in three of them. Adjust your perception of him as you see fit.

When it comes down to it, I can't look at Cook as a truly top reliever because he just walks too many guys. At his best, he's walking three batters per nine innings, and last year that rate jumped to four batters per nine. That's just too many free baserunners to be handing out when you're trying to protect leads, even if you generally keep the hits down. It's not that I don't think Cook is good, it's just that I think he's replaceable and that the time to strike is now before his health goes south.

The current bullpen

Let's see what the A's have in their pen right now:

Sean Doolittle

Ryan Cook

Dan Otero

Eric O'Flaherty

Fernando Abad

Eury De La Rosa

R.J. Alvarez

Chris Bassitt?

Taylor Thompson

Evan Scribner

Pat Venditte

Would the A's have enough without Cook? Start with Doolittle, Otero and Abad as a great core. You can keep O'Flaherty as a fourth, or you can trade him as well and let De Le Rosa step into his role as the third lefty. Alvarez makes five, as he seems ready to take on an MLB role. I don't know what the team plans to do with Bassitt, but he could be another strong option. There's always Pat Venditte, the ambidextrous pitcher. Another starter who doesn't make the rotation, like Sean Nolin or even Jesse Chavez, could need a job. The pen is likely to be crowded with good options as it is, and that's before getting to emergency backup plans like Scribner and Thompson who could be gone if they don't make the roster. Keeping Cook just exacerbates the logjam, and it specifically blocks Alvarez from growing into the set-up role that I assume he was acquired to eventually fill.

I alluded to it in the above paragraph, but I could write a similar article regarding O'Flaherty. He showed enough last year to prove that he's recovered from his Tommy John operation, he's quite expensive ($5.5M), and he has an obvious left-handed replacement waiting behind him in De La Rosa, who was acquired from the Diamondbacks a few days ago. De La Rosa will be just 25 next season and had solid numbers for Arizona last year. However, that situation is complicated by O'Flaherty's surgery recovery and perhaps Beane would rather just gamble on him having a best-case year on the field.

But to whom, and for what?

Unfortunately, I don't have any answers to those questions. I don't have a specific team or player in mind with which to construct a Cook trade. But Beane hasn't had any trouble finding takers for his All-Stars this winter, and nobody is ever happy with their pitching staffs in December. I don't know if a reliever of Cook's caliber gets you anything on his own, or if he has to be part of a larger win-now package with, say, Jaso, but there must be some trade value in a late-20s set-up man with a lot of velocity and strikeouts and an All-Star resume. Even if it's just another minor league reliever to keep the chain going, I'd still be interested.

Ryan Cook pitched like a great reliever for two years in Oakland. However, I think he was a little bit over his head and that he'll be more like a good reliever in the coming years. Between that decline and my own questions about his health, plus the crowded bullpen, the presence of an obvious young replacement, and the imminent escalation of Cook's salary, I think this is the time to trade him for whatever can be acquired. As is the theme of the offseason, a Cook trade could make the A's better in the future without costing any on-field production in 2015.