Big Four crumbling as we know it?

In case you hadn’t noticed, the tight little group of ATP players who once were called the Big Four have been fruitful, and they’ve multiplied: It’s now more like a Big Six or Eight … and counting. It raises the question: Are we in the midst of a major ATP transition?

Last week, we finally kicked off the European clay-court swing with the closest thing tennis has to news, a real “man bites dog” story. Top-seeded Rafael Nadal lost in Monte Carlo, where he was 50-2 for his career (with eight titles) -- until No. 6 seed David Ferrer bushwhacked him in the quarterfinals, thereby improving a dismal head-to-head record with Nadal to 6-21. What’s this world coming to, when Ferrer beats Nadal in Monte Carlo?

Novak Djokovic, the No. 2 seed and defending champ, relapsed after winning the two big U.S. hard-court Masters. He got his Belgrade rung in the semifinals by No. 4 seed Roger Federer, who's still as dangerous as a cobra, with Nadal the only reliable mongoose on the tour.

Andy Murray -- remember him? -- is down to No. 8 in the rankings. He decided to keep his powder dry for the upcoming Masters events and Roland Garros by taking a pass on Monte Carlo.

Stanislas Wawrinka, who’s moved ahead of Federer on the Swiss national team’s depth chart, won Monte Carlo. He thereby built on his No. 3 ranking and added to his street cred as a guy who’s fully prepared to take his place alongside the only three men who have won Grand Slam singles titles since Juan Martin del Potro won the U.S. Open in 2009 -- Nadal, Djokovic, Federer and Murray.

With Wawrinka now joining the elite, will Tomas Berdych and Jo-Wilfried Tsonga, respectively Nos. 5 and 12 in the rankings, be shamed into making their long-anticipated breakthroughs as Grand Slam winners this year? When pigs fly, you might think. You might have had the same reaction, though, if I’d asked whether Ferrer can beat Nadal at Monte Carlo.

It’s too early to theorize that the fortress of the Big Four is crumbling, but there appear to be cracks in the wall. Federer may be demonstrating that there are all kinds of “senior moments,” not all of them bad. But though he’s climbed back and hangs in there at No. 4, Federer is, after all, 32 years old. Djokovic can’t seem to hang on to that 2011 feeling, and Murray seems in no hurry to win titles again -- heck, he seems in no particular hurry to play matches, as demonstrated by his withdrawal from Monte Carlo despite all the ranking points on offer.

This week won’t advance this theme significantly, because Nadal and Ferrer are the only members of the top 10 who will be playing in the Barcelona ATP 500. It’s easy to overlook this tournament, wedged as it is between Masters 1000 events, but it means a lot to the Spanish players and public. It’s the closest thing you can have to an invitational for the cream of the Spanish crop, and all the top men from that nation are entered. If you were wondering why Nadal bothers to play this event, there’s your answer, or at least part of it -- pride.

On the heels of that loss to Ferrer in Monte Carlo, Nadal now is officially more successful at Barcelona. He’s won it eight times in nine tries, just to make sure all those other Spanish dudes remember who the boss is. Nadal is the least shaky of the Big Four, but the fact remains that he hasn’t won a tournament since Rio in mid-February. He’s been a bust in his last three events -- all Masters 1000s, including one on clay. If Nadal doesn’t get the win this week in Barcelona, we’ll embark on the heart of the clay-court season in more exciting disarray than we’ve experienced in a long while.

The walls of the fortress may still be pretty solid, but cracks are always more likely to expand than to close up.