Llorente, who has been linked with several top European clubs this summer, had been given an extended holiday after Spain’s European Championship win, for which he was an unused squad member.
He is expected to feature in Athletic Club’s Europa League qualifying legs against Slask Wroclaw on August 2 and 9.
Defender Mikel San Jose also returned to training and will be available for the matches.
The former Liverpool centre-back had been out of action with chickenpox. The illness had forced him out of Spain’s Olympic squad.
Both players trained without the ball on Friday and Llorente will feature in full training from Monday.