This article is part of our Rising Star Portfolios series.

On Dec. 1, I highlighted two stocks that I was seriously considering adding to my real-money Motley Fool portfolio: Telefonica (NYSE: TEF) and Banco Santander (NYSE: STD).

My thesis was simple: Spain was already getting called out as the next domino to fall in the eurozone debt debacle, and despite its many problems, I felt the calamity wasn't as bad as it was being made out to seem. In addition, the two companies mentioned above seemed fundamentally solid to me, and I thought they offered high upside with limited downside.

What I bought and what I didn't
You can read my ultimate buy recommendation here, where I ended up adding a $1,000 position in Telefonica to my portfolio.

It was a difficult decision to make, but in the end, I chose (at least for the time being) to stay away from Santander and other eurozone banks.

First of all, when I wrote that Santander was on my radar, the stock was trading somewhere between $9 and $10. I felt this was a pretty good deal; not far off from its 52-week low in fact. However, by the time I decided to make my buy recommendation, the stock had increased to above $11, and it closed yesterday at $11.28. That's nearly a 15% increase in a very short period of time. Other prominent banks also saw big jumps: During that same period, Bank of Ireland (NYSE: IRE) shot up by 75%, and National Bank of Greece (NYSE: NBG) saw a steady 6% gain.

That 15% price gain was enough to turn what I'd previously thought was a screaming value play into what I considered a good buy, but not good enough to make such a big bet on a scary industry.

Even though I consider Banco Santander to be one of the greatest banks in Europe right now, I'm totally baffled by how the EU is handling the entire sovereign debt crisis. Despite Ireland's well-publicized economic woes and enormous bailout, its banks are still acting as if all is well. Allied Irish Banks (NYSE: AIB), which is expected to be 95% state-owned, is ready to hand out more than $50 million in bonuses next week -- not exactly the prudence you'd like to see from an institution depending on bailouts for a lifeline. And frankly, it's difficult to keep track of who's behind the bailout and who's not. Almost every country acknowledges the necessity of a bailout and the determination to keep the euro up and running, but frugal countries like Germany are getting fed up with having to baby-sit their spendthrift siblings.

But most importantly, I'm just honestly scared to invest in another eurozone bank right now (despite my earlier investment in National Bank of Greece). Troubles with other countries such as Portugal and Italy have yet to really surface, and by no stretch of the imagination is Greece out of the woods. Any sort of currency crisis or domino effect could knock Spain for a loop and could also have the effect of destroying value for the assets of Santander. Will Santander need a bailout? Absolutely not. Is it one of the most well-run banks I've seen in the last year? Absolutely.

I'm just not ready to take that plunge yet -- but stay tuned as I follow this one closely.

How do you feel -- would you invest in Banco Santander? Feel free to let us know in the comments below!

This article is part of our Rising Star Portfolios series, where we give some of our most promising stock analysts cold, hard cash to manage on the Fool's behalf. We'd like you to track our performance and benefit from these real-money, real-time free stock picks. See all of our Rising Star analysts (and their portfolios).

Jordan DiPietro owns shares of National Bank of Greece. The Fool owns shares of Telefonica. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool's disclosure policy needs to dance itself clean of all this euro nonsense.