Rafael Nadal heaped praise on conqueror Stan Wawrinka, who ousted the Spaniard from the Internazionali d'Italia.

Nadal's French Open preparation took yet another hit as Wawrinka posted a 7-6 (9-7) 6-2 victory in Rome, the Swiss' second straight victory over the former world number one.

After his final competitive match before he begins his bid for a 10th title at Roland Garros, Nadal simply hailed Wawrinka's aggression in their quarter-final.

"I didn't have enough leg in some moments today. He played crazy. He hit amazing shots in a lot of moments and especially important ones," Nadal said. 

"I am not very happy with the way I played. 

"During the night the ball is bigger, the bounces are not that high. So he has the chance to go for it. And he was on fire."

The loss will ensure Nadal is not among the top four seeds in Paris.