MADRID (AFP) - US Open finalists Marin Cilic and Kei Nishikori have pulled out of tennis' Valencia Open next week owing to personal reasons, with the Croatian now guaranteed a berth at the World Tour Finals in London.

Cilic, who beat Nishikori to claim his first Grand Slam title in New York last month, is certain of a debut appearance at the Finals as Grand Slam winners are assured of their place as long as they are ranked in the world's top 20.

Nishikori should also mathematically secure his slot in London in the coming weeks as he has risen to fifth in the season standings with victory on home soil at the Japan Open earlier this month.

Two-time Grand Slam champion Andy Murray and former French Open finalist David Ferrer are still in need of points to make it to the English capital and could meet in the semi-finals in Valencia.

Murray will start his campaign against Austrian Juergen Melzer, while top seed Ferrer takes on Italy's Andreas Seppi.

On the other side of the draw, second seed Tomas Berdych plays Spain's Pablo Andujar in the first round.