Who says the world of professional tennis doesn’t have an off-season? The Australian Open ended five weeks ago, and in that time, Roger Federer hasn’t played a single match. He visited the Nike headquarters in Oregon. He went to the Super Bowl. He probably bought a lot of designer clothes, caught up on a few novels or movies, and had an extra glass of wine or three with his dinners.

At last, the world no. 1 returns to action this week in Dubai, where he has trained and lived for several years. We’ll find out early what sort of condition he’s in: The Dubai field is usually quite strong because the tournament shells out top dollar in appearance fees (the prize money is on the smaller side). This year, “strong” is a weak word. The field is loaded: Rafael Nadal, Novak Djokovic, David Ferrer, Nikolay Davydenko, Andy Roddick (for the first time), Richard Gasquet, and Tomas Berdych will be in attendance. That’s eight of the world’s top 10, plus several other dangerous players, including Tommy Haas, Mikhail Youzhny, Juan Carlos Ferrero (who plays Roddick in the first round), and Federer’s first opponent, Andy Murray, who has won two tournaments this season and beaten Federer once before.

But Dubai is just the beginning. The next nine months will be the most demanding of Federer’s career. From Dubai, Federer flies to New York for his March 10 exhibition against Pete Sampras at Madison Square Garden. He’ll then leave for California for the Pacific Life Open in Indian Wells, which begins later in the week. The Sony Ericsson Open in Miami is next, followed by a week off, and then the clay court season. Federer has added Estoril, Portugal, to his schedule this year in hopes of fine-tuning his clay skills for the French Open, the only major he has yet to win. All told, from this week through Wimbledon, he’ll play 10 tournaments and one exhibition and have only between five and six weeks in which he doesn’t play matches (if you count the days before Indian Wells and Miami, which give top players a bye).

Federer’s summer and fall are packed, too. He’ll take a couple of weeks off after Wimbledon before flying to Toronto, Cincinnati, Beijing (the Olympics), and back to New York for the U.S. Open. He’s scheduled to play one more tournament than usual this fall, in Stockholm; if he sticks by this plan, he’ll play tournaments four weeks in a row from October to early November in Europe and then finish the year off at the Masters Cup in Shanghai. In all, it’s an ambitious and potentially grueling schedule that Federer won’t ever attempt again — by the time the next Olympics arrive, in 2012, he’ll be 31 and likely won’t play as often leading up to it.

Since he became the no. 1 player in the world four years ago, Federer has mostly glided along. He’s won 10 of the 15 majors he has played, dominated most of the game’s best players (he’s beaten Roddick and Lleyton Hewitt each 11 consecutive times), and sustained nary an injury (an ankle injury in late 2005 was the only one of note). It’s hard to imagine him finishing off this season without at least a few scrapes, and the intensity of his schedule — which he might reduce at any moment along the way — is just part of the reason.

Federer now has two legitimate no. 1 players, Nadal and Djokovic, behind him. Both men are in position to take over the no. 1 ranking this year. Both of them can test Federer on every surface. Both are at least five years younger. In Dubai this week, Djokovic and Nadal are on the same side of the draw, so they’ll have to contend with each other before earning a shot at Federer. More often than not, though, at least one of them will stand in Federer’s way as he tries to tie, and eventually break, Sampras’s record of 14 major titles (Federer now has 12).

Many a tennis observer has flirted with the idea that Federer’s dominance the last few years might be attributed to a weaker field than the game had in Sampras’s prime. I tend to think Federer’s excellence has made his colleagues look second-rate, but either way, there should be no debate about what he is up against now. In Nadal and Djokovic, tennis might very well have the two most talented, versatile, hungry, and fiercely competitive no. 2 and no. 3 players who have ever competed at the same time. No doubt the next two major titles will be the most difficult for Federer to win. By the time August rolls around, he’ll be thankful for all the rest.

Mr. Perrotta is a senior editor at Tennis Magazine. He can be reached at tperrotta@tennismagazine.com.