The Madrid Open, the fourth tournament of the ATP World Tour Masters 1000 series, is underway with some of the biggest names in tennis set to meet. Andy Murray defends his title against the surging Rafael Nadal and world No. 1 Novak Djokovic, but one of the most recognizable names in the sport will be absent.

On Monday, Roger Federer withdrew from the tournament due a back injury, and after some recent physical setbacks. Federer, ranked No. 3 but without a tournament title in 2016, is coming off a loss to Jo-Wilfried Tsonga more than two weeks ago in Monte Carlo. The Swiss star has only played in three tournaments this year, and his participation in the Spanish capital was always somewhat in doubt with his late addition to the field and with the French Open just weeks away.

Federer, who last won the Madrid Open in 2012, described the back injury as “normal back things I've had in past.” He also suffered a knee injury in a home accident in February, which required surgery, and also skipped the Miami Open due to the flu.

"I'd rather play it safe and get ready for Rome,” the 34-year-old said about missing the Madrid Open. “If I can't play Rome, it's not the end of the world, but hopefully I'll get to play.”

Nicolas Mahut or Joao Sousa were slated to face Federer after his first-round bye.

While Federer is often a frontrunner to win tournaments on red clay, he was never considered a favorite in Madrid. According to, Djokovic now enters as the clear favorite at 10/11, followed by Nadal at 5/1 and Murray at 10/1. Stan Wawrinka, who will defend his French Open title next month, has the fourth-best odds at 18/1 followed by Kei Nishikori at 20/1.

Djokovic, whose lone Madrid title came in 2011, will face the winner of Nicolas Almagro and Borna Coric with a potential date with either Spaniards Feliciano Lopez or Roberto Bautista Agut waiting in the quarterfinals. The biggest threat for Djokovic to reach the final should be Nishikori, or the winner of Tsonga vs. Wawrinka, when they meet in the Round of 16.

The other half of the draw got less difficult with Federer out, but still has two elite competitors. Nadal, a four-time winner of the tournament, will face Andrey Kuznetsov, who defeated Viktor Troicki in straight sets. Looming for Nadal is a potential semifinals date with Murray, who defeated Nadal in straight sets in last year's final. Nadal and Kuznetsov will meet on Tuesday, but not before 10 a.m. ET.

Nadal, who has been in strong form in recent weeks with titles in Monte Carlo and Barcelona, is seeking his third title in Madrid in four years. Murray faces the winner of Radek Stepanek and Vasek Pospisil on Tuesday.

Here’s a look at the entire draw and Monday and Tuesday's schedule.