Miami, Apr 3 (IANS): The tennis world is turning its attention to the clay court season, with the field wide open due to the absence of Swiss great Roger Federer and Argentina's Juan Martín del Potro, as well as questions about the health of Spain's Rafa Nadal, the undisputed "king of clay."

Nadal, the World No. 1, may make his return to the court from a leg injury next weekend, when Spain take on Germany in a Davis Cup tie in Valencia, reports Efe.

The Spanish star, a 16-time Grand Slam champion, has been bothered by the leg injury since the Australian Open and again injured the leg in Acapulco.

Nadal faces a tough challenge since he will be defending 4,680 points after winning titles on red clay at the French Open, Monte Carlo, Madrid and Barcelona last year.

The Spaniard regained the top spot in the ATP rankings with 8,770 points, while Federer, who is once again skipping the clay season to focus on the grass court events leading up to Wimbledon, has 8,670 points.

Federer was the World No. 1 until the Miami Open, where the defending champion went out in the second round, losing 990 points.

The Swiss legend, however, has no points riding on clay, while Nadal will have to equal his 2017 performance to stay in the top spot, a difficult task at best.

On the women's side, Romania's Simona Halep, the world No. 1, won Madrid, was the finalist in Rome and went down in the semis last year in Stuttgart.

Danish World No. 2 Caroline Wozniacki and Spanish World No. 3 Garbiñe Muguruza, the 2016 French Open champion, will also be in the mix.

Latvia's Jelena Ostapenko, the defending French Open champ and finalist at the Miami Open, will also be bringing her hard-hitting game to the chase for glory on clay.