The world No 2 was due to face his toughest test to date in Spain, having struggled past Nicolas Almagro before a before straightforward victory over Feliciano Lopez.
But ahead of their Friday quarter-final showdown, world no 8 Nishikori suffered a recurrence of the wrist injury that has troubled him in recent months and with the French Open on the horizon, the Japanese has opted against taking a risk.
"I will plan to play Rome, but we will see." said Nishikori.
"I cannot promise to play or pull out right now. [The] French is more important."
