This week, in the run-up to Wimbledon, I’ll dispense with the customary preview mechanics in order to focus on what I would call the uncomfortable questions that loom over the tournament. Think of them as questions nobody wants or thinks to ask in the midst of all those animated conversations about the favorite sons (and daughters) as the tournament approaches. So let’s start this off with the first question that ought to make some of you fidget and squirm:

Who among the “Big Four” is in the most perilous situation (comparatively speaking) as the tournament approaches?

It’s funny, but if you put this question out there a week ago, you would almost reflexively say it’s a toss-up between Andy Murray and defending champion Roger Federer. That’s because Federer left the French Open (after losing to Jo-Wilfried Tsonga in the quarterfinals) still looking for his first tournament victory since last year’s Cincinnati Masters, almost 10 months ago. Murray, for his part, looked to be in serious trouble after pulling out of his first match in Rome, with a back injury that subsequently forced him to pull out of the French Open.

But those men boosted their stock considerably with title runs last week. Concerned about his future just a few weeks ago, Murray made it through some familiar trials at Queen’s Club. He endured rain delays, slick courts, and all the bending and lunging required on grass in excellent shape. Looking ahead to Wimbledon after dispatching defending champ Marin Cilic in the final, the Scot said: “To come through after the last three, four weeks is really, really nice. The most important thing, next week or so, is just to make sure I keep improving the strength of my back. I’m in a good place and I just keep working hard the next week.”

A runner-up at Halle a year ago, Federer went back to a familiar well and pulled up a bucket containing his sixth Halle trophy. He beat Tommy Haas, who Federer lost to in Halle last year, along the way, and took out Mikhail Youzhny in a three-set final. It was just the fourth set Youzhny has won from Federer in 15 meetings going all the way back to 2000. Federer has won all those matches—but that’s not even the best part.

Most of you know this is the 10th anniversary of seven-time Wimbledon champion Federer’s first triumph that the All England Club. He also beat Youzhny at Halle in 2003. Furthermore, Federer counted coup on the racquet-smashing Russian during his title run last year, too. Karma, or mere coincidence?

“Ten years ago I went into Wimbledon with so much pressure,” Federer said after winning at Halle. “Even though I had lost in the first round the year before I needed to prove my point, that I was a legitimate Grand Slam contender. I had incredible pressure. Now, ten years later, I know Wimbledon, I know Halle, and I know what I need to do to perform well. I’m going in with pressure because I'm defending my title.”

Clearly these two men are not just arcing upward, they’ll also be in a comfort zone at Wimbledon. Federer because of his personal history in London’s SW19 postal zone, and Murray because he recorded his first major win on those same courts when he won gold in last summer’s Olympic Games. And Murray appears to have already cleared what once appeared to be the largest hurdle of his career, the circus-like atmosphere and pressures that would surround him as, potentially, the first British man to win Wimbledon since Fred Perry did it over 75 years ago.

The two men who have split the Grand Slam titles offered thus far this year haven’t given us much to go on when it comes to Wimbledon. Top-ranked Novak Djokovic chose to recover and re-apply himself after losing an epic French Open semifinal to the now fifth-ranked Rafael Nadal. As Djokovic said shortly after that defeat, “I wanted this title so much, so I am disappointed. That's it. That's the way I feel. (But) I don't think it's going take the toll on me in the future because I have been in these particular situations before.” He added he will use the time off between majors to “mentally get motivated and inspired” for Wimbledon.

Djokovic’s main challenges appear to be mental and emotional, while Nadal’s own concerns never stray very far from the physical. Rafa pulled out of Halle before he successfully completed his mission to win an eighth French Open title, but we know by now that those problematic knees are a constant source of anxiety for Nadal. My Spanish sources told me that Nadal’s personal physician told him in no uncertain terms to pull out of Halle to spare his knees, whereupon Rafa went home to relax for a few days.

Djokovic and Nadal are both taking a calculated risk by embarking on Wimbledon with no competitive matches on grass, but the Serb did so the past two years, winning the title in 2011 and losing to Federer in the semis last year. Nadal appears to be assuming the greater risk, because he’s played at either Queen’s Club or Halle for the past two years, raising an interesting question: Did his experience last year, when he won at Roland Garros and played Halle before Lukas Rosol blasted him off Centre Court, leave him gun shy on grass?

Nadal’s knees were aching by Wimbledon time last year; the fact that he took over seven months off after the loss to Rosol confirms just how serious the injury was. That might be enough to make Nadal as skittish as a cat next week, despite the confidence, joy, and relief he experienced when he won Roland Garros.

As reliable as Nadal has been (at least before his knees began to act up) and as brilliantly as he’s performed at Wimbledon throughout his career, the tournament has also been unkind to him at times. Nadal has won the title twice, and it was the scene of his finest moment in tennis—the 9-7 in-the-fifth win over Federer in the 2008 final, a match that many pick as the greatest of all-time.

But time flies, and 2008 was a long time—and many painful injections and therapy sessions—ago. Nadal was unable to defend his crown the following year, but he rebounded to win his second title in 2010 with a win over no-slam-wonder Tomas Berdych. As proud as Nadal has been to shatter the “clay-court specialist” label, and to topple an icon like Federer, he lost the only completed match he’s played at Wimbledon with Djokovic (the 2011 final), and he’s still 1-2 there against Federer. On the other hand, he’s 3-0 against Murray at Wimbledon, but that’s more of a problem for the Scot than a solution for Nadal.

In Paris, Nadal left the impression that reasserting his towering superiority on clay was of utmost importance to him. He may be due for an emotional letdown, and the constant stress about his knees can’t be a good omen for him. Since Wimbledon won’t be elevating him in the seedings, Nadal might once again be faced with meeting a top seed in the quarterfinals.

As outstanding as Rafa’s record is at Wimbledon, the questions about his physical condition, preparation, and recent history on grass suggest that while Djokovic is still licking fresh wounds, while Murray might still be the least likely to win at Wimbledon, and while Federer has succeeded in just one of his last 13 majors, the player most likely to absorb a shocking loss during the fortnight is Rafael Nadal.