Former world No.3 Nikolay Davydenko pulled out of his Malaysian Open quarterfinal against Japanese third seed Kei Nishikori on Friday.

The Russian had lost the first set 6-4 when he retired from the match. The reason was unclear.

Nishikori, ranked 17 in the world in his breakthrough season, plays second seed Juan Monaco in the quarterfinals. The Argentinean downed Canada's Vasek Pospisil in 6-3, 6-4, in their quarterfinal.

The 31-year-old Davydenko, who recently refuted rumors he is close to announcing his retirement from the game, had ousted lucky loser Sanam Singh of India and Uzbekistan’s Denis Istomin to make the quarterfinals.

The prize fund for the hard court tournament is $850,000.