A look at David Ferrer’s results from the second half of 2013 suggests a sudden plunge in the form of the world No. 4. After all, in the first half of the year he won two titles and almost never lost in early rounds (or to players not named Rafael Nadal). Since losing in the Roland Garros final, however, Ferrer has not reached a semifinal and has lost to unheralded figures from Dmitry Tursunov and Alex Bogomolov, Jr. to Joao Sousa and Florian Mayer.

Granted, the fast hard courts in recent weeks are Ferrer’s weakest surface. It has been especially impressive each year when he can win indoor tournaments and even beat other top players on this surface. The shock should be that he has done so well in most years, not that he has been so poor this year.

But that is exactly who Ferrer is. He is the ultimate grinder, just keeping his opponents in uncomfortable positions until he finds a winning position. This is what Ferrer has done in match after match. Thus, it should no longer shock us when he does it, even on uncomfortable surfaces.

So why has Ferrer stopped doing that? It is not just the number of losses that he has accumulated this summer and fall, but how they have unfolded. This consummate competitor has been hit off the court by players who normally lack the ability to him off the court. His own unforced errors do not seem to have risen appreciably. He just isn’t playing as well as he was before.

In a mirror-image sense, Ferrer’s decline this year recalls Djokovic’s rise beginning in 2011. When Djokovic launched himself to the top of the sport, there was nothing specific in his game that you could point to that he had improved on. His shots were the same; they were just better. His fitness and breathing might have improved, but the fact remained that Djokovic did everything on the court just a little bit better than he had in 2010. The Serb made no dramatic changes to his playing style. You couldn’t point to a particular forehand or backhand and say, “That’s what Djokovic was missing.” Instead, every ball was struck a little more cleanly, a little deeper, and they were all tougher to handle.

Ferrer this year seems to have undergone the same transformation in reverse. His shots are not significantly different from before. He does not spray errors in most situations where he used to hit winners. He is simply a shade less crisp and clean on court. His grinding style of play now forces his opponents into slightly less awkward situations, and a game of inches like tennis means that every small difference counts.

We can only guess what caused this decline. For a player as physical as Ferrer who has entered his 30s, we could guess that the daily grind is hurting him. But he is not getting weaker as weeks and tournaments go on. He is losing early matches to players that he usually should be able to cruise past. Maybe the foot injury that bothered him at Wimbledon is still there, but one would have expected Ferrer to take time off to fix it if that was true.

Or maybe, and this should be the scariest possibility for Ferrer fans, he really was not as upbeat after that Roland Garros loss as he seemed. For someone who grinds himself past his opponents, confidence is everything. Similar to Caroline Wozniacki on the women’s side, Ferrer will struggle if he lacks the confidence that he can retrieve every ball and play his counterpunching game to perfection. So maybe there is something lacking there. Maybe coming so close to what would have been the culmination of his career has unsettled him. Maybe he is still haunted by those moments in that final where he had opportunities but missed them.

Whatever the cause, Ferrer must emerge from his slump soon. He has many points defend in the upcoming weeks, especially as the defending champion of the Paris Masters 1000 tournament.  If his decline continues into next year, he could see his ranking slide very quicly.