There is another aspect as to why the Cubs don't bring up players like Armando Rivero and Kris Bryant -- and that aspect is roster management.

There is a finite amount of space on a roster and you have to manage that space as best you can. Sometimes that means delaying one call-up so that you can protect a player later so that you don't lose him in the Rule 5 draft.

With the Cubs increasing their talent level the past 3 years, roster management becomes more important than ever. In the past they have lost utility infielders Marwin Gonzalez and Ryan Flaherty, but that could change. They don't want to be the team that loses a Hector Rondon-type player. Perhaps less direct is the missed opportunity to develop a player. Players gets drafted before they become a finished product. It's possible that player could have developed differently had he stayed in the minors -- and even if he didn't have a future with the team, there is the possibility that he could have developed some trade value in the minors. Let's use a player to illustrate what I mean. What if, for example, Marco Hernandez takes a step forward in AA with his offense? A slick fielding SS with even an average bat has value on the market. But if you lose that player then you lose that value as well. A good organization is not in the business of giving away value for nothing in return.

This isn't a case of choosing between two players and deciding who is more valuable. Kris Bryant is obviously more valuable than Marco Hernandez. You aren't sacrificing Bryant for the sake of Hernandez, you are sacrificing one month's worth of Bryant in a non-contending season for Hernandez's career in the organization and/or potential future trade value. Considering that month also has significant financial ramifications for the Cubs and their ability to control payroll costs, it becomes a rather easy decision to not call-up Bryant.

Rivero is a better example, however, because the delay in his call-up has nothing to do with finances. It is strictly about conserving roster space. The Cubs don't need to have a month of Rivero this season at the expense of losing a player like Hernandez in December.

Now, I am only using Hernandez as an example but we can use any number of Rule 5 eligible players to illustrate. Let's take a look at some of the more talented players who are vulnerable to the Rule 5 draft this year. You can see the full list at The Cub Reporter.

Keep in mind that the Cubs have already decided to protect would be eligibles Kyle Hendricks, Eric Jokisch, and Rafael Lopez by virtue of their early call-ups.

We have mentioned often that there are two basic types of players to protect.

Near MLB ready players who could contribute and have some upside, probably as role players. Higher upside players who are not MLB ready but have some useful skills (i,e. speed, versatility, defense) that makes them useful as a 25th man until the team can send them back down the next season.

Here are the players that best fit those descriptions...

Gioskar Amaya, 2B, Daytona (A+)

Jeffrey Baez, OF, Kane County (A)

Zach Cates, RP, Tennessee (AA)

Hunter Cervenka, RP (L), Tennessee

Gerardo Concepcion, RP (L), Daytona

Willson Contreras, C, Daytona

CJ Edwards, SP, Tennessee

Marco Hernandez, SS, Daytona

Andrew McKirahan, RP (L), Tennessee

Carlos Penalver, SS, Kane County

Ivan Pineyro, SP, Tennessee

Won't be protected:

Jeffery Baez is too raw and does not give enough value on defense as a corner OF'er to have any chance of sticking on a 25 man roster. He has some upside but not enough for a team to give up full year's worth of a roster space while taking a year away from much needed development.

Willson Contreras' appeal comes from his athleticism, raw talent, and the scarcity of catching prospects. An off year makes it pretty certain the Cubs won't protect him, especially since the Cubs have since acquired Kyle Schwarber, Mark Zagunis, and Victor Caratini to fill the gap, not to mention the emergence of Will Remillard and Cael Brockmeyer as potential prospects. It's unlikely a team takes Contreras given his poor hitting performance, but had he hit well, his athleticism, surprising speed and ability to play the OF might have made him interesting as a 3rd catcher/25th man.

Carlos Penalver is a slick fielder but he did not hit at the low A ball level and is still too young and erratic to be of much value as a defensive replacement.

On the bubble:

Gioskar Amaya is a mature beyond his years player who can be an asset defensively at 2B. He has a good approach at the plate and enough bat speed to hit MLB quality fastballs with regularity. He has not shown much extra base power this year but does have the potential for gap power, especially to his pull side. Amaya is respected in scouting circles and some team may take a chance. What works against him is that he is essentially a 2B only and doesn't have great use as a utility if he has to come off the bench. There is some risk of losing him and he has value in this organization, so the Cubs may choose to protect him even if he isn't close to being MLB ready and appears to have his path to the big leagues blocked by a number of more highly regarded prospects.

Zach Cates showed tremendous progress with his fastball command at Daytona and was one of the team's most reliable relievers in the first half. He struggled some at Tennessee but showed flashes there as well. Cates can hit 96 mph to go with above average athleticism. That alone will draw some attention from scouts. The Cubs will get a longer look in the AFL to determine whether they should protect him or take their chances.

Hunter Cervenka has a power arm (low 90s with sink/tail, high 80s cutter) and he's lefty, so that alone makes him a risk to be taken. He has been exceptionally tough on LH hitters this year, making him attractive as a potential LOOGY for now. The key for him is command/control. Cervenka showed some progress in that area but was streaky in that regard.

Gerardo Concepcion has come a long way and has been in the low 90s at times this year, flashing an occasionally good breaking ball that drew swings and misses when I saw him at Kane County. He was an effective starter in Cuba's highest league, the Serie Nacional, so he is not your typical A ball prospect. He has a good chance of holding his own as a lefty reliever in the short term. The Cubs are sending him to the AFL to get an extended look and to make up for some lost innings. If he can hold up physically, he has the potential to be a back-end starter, so that may increase his value even more.

Marco Hernandez isn't ready for the bigs but he is a talented defender and good athlete with some speed. That alone gives him pretty good utility value for a year, after which a team can send him down again and hope his bat develops enough to make him a starter. Hernandez made some great strides in terms of his maturity and his hit tool this season. Is it enough to make him a potential Rule 5 casualty? That's a decision the Cubs will have to make.

Andrew McKirahan has a live fastball (I saw him sit 92-93 at Kane) and a good breaking ball. He misses bats with regularity (just under 8 Ks/9 IP) and this year he has kept the walks down to under 2 per 9 IP (around the 5% range). The difference is that he stayed healthy this year. His dominance at Daytona (0.99 ERA/2.76 FIP) and continued strong performance at Tennessee (3.45 ERA/3.50 FIP) certainly drew some attention and his left-handedness will probably get him a look.

Ivan Pineyro was injured much of the season (shoulder) and didn't pitch well when he was on the mound (5.55 ERA/4.85 FIP). He is a finesse starter with a high 80s fastball and a good change, so he depends on good command. That did not happen this year and Pineyro got hit hard. The Cubs liked Pineyro when they acquired him and sending him to the AFL is in part to give him another look and also to make up for lost innings. My guess is he won't be protected as many teams have similar pitchers and Pineyro hasn't done much to convince anyone he is close to being ready. Most would agree he has the poise and maturity to handle the jump, but physically he needs development, particularly with his command and breaking stuff.

The lock:

CJ Edwards: Do I need to explain why? Edwards is a top 100 prospect with electric stuff when healthy and the central piece in the deal that sent Matt Garza to Texas.

The Cubs probably have a good idea of who they'd like to protect but it is impossible to say with any certainty how much space they will need this offseason. Will they want to leave a space open to facilitate an early free agent signing? Can they get what they want without losing a roster spot via a trade? There are still questions to be answered. Those questions include the players the Cubs may remove from the roster to make room.

Players who will come off the 40 man roster

Carlos Villanueva is a free agent and he will open up a spot, so we need not worry about protecting CJ Edwards, who is next in line for a roster spot. The rest of the roster composition will depend on the following decisions....

Here are the other players who could be on the outside looking in when decision time rolls around...

Josh Vitters: The Cubs have cut the cord with their other former Pre-Theo top prospect, Brett Jackson. Could Vitters be far behind. A poor season at AAA which showed no improvement in his plate discipline or defense makes it likely that the Cubs consider him a poor fit for their 25 man roster. I have questioned his commitment to development in the past though I don't know if the Cubs feel the same way. Add that he is out of options in 2015 and this is close to a no-brainer for a non-tender.

Chris Rusin: His non-call speaks volumes, though publicly the Cubs would probably say he reached his innings limit. That may be true, but if Rusin was a part of the plan the Cubs wouldn't have let it get to that point. He also has less innings than other pitchers who did get the call, most notably Eric Jokisch. The addition of Jokisch and Felix Doubront as LHPs to the 40 man roster give even more indication that the writing may be on the wall here.

Chris Valaika: Valaika got a much deserved reward with a call-up but the job security of replacement level utility infielders with no options on 40 man rosters is tenuous. The Cubs will not hold on to Valaika if roster space is needed. They can either bring him back on a minor league deal or find a similar player who will.

Kyuji Fujikawa: He had a vesting option which did not vest. Now it becomes a club option for $5.5M. The Cubs have little to show for their investment because of Fujikawa's unfortunate early injury, but the option presents little value for them right now. The guess here is they decline that option and allow him to become a free agent. They may still bring him back, but the free agency at least opens up some short term space.

Zac Rosscup may be getting an audition for his roster spot this September. You have to like the 90-94 mph FB and the slider, both of which are swing and miss pitches, but his inability to throw strikes makes him a question mark. The Cubs have another lefty in McKirahan who doesn't miss quite as many bats, but does throw hard and throws more strikes. Still, it's hard to give up on a lefty with Rosscup's good stuff. He would undoubtedly get picked up quickly by a team that thinks they can coach him up.

John Baker: The popular backup is great in the clubhouse, but below replacement level on the field. That makes him a non-tender candidate that the Cubs could try to bring back on another minor league deal.

The Cubs could easily open up as many as 5 spaces without affecting the 2015 roster. It's possible they will leave one open, either for the Rule 5 Draft or to give them the flexibility to sign a free agent quickly. But they could always wait to make those changes until it's needed.

It's difficult to know how many players the Cubs will protect but CJ Edwards is certain to be one of them. The Cubs will then have 3-5 spots to consider with Gerardo Concepcion, Andrew McKirahan, Gioskar Amaya, Marco Hernandez, and Zach Cates as my early favorites, but things are certain to change and we'll learn more as the season/offseason unfolds.