Former Arsenal midfielder Santi Cazorla wrote on Twitter that "he felt like a footballer again" after returning to preseason training with Villarreal.
Cazorla, 33, is hoping to be fit again after missing 20 months with a right Achilles injury that required a total of 10 surgeries and a skin graft from his arm.
"Happy to feel like a footballer again, there's still a lot of work ahead," Cazorla wrote. "With more enthusiasm than ever."
Villarreal, meanwhile, posted a video of Cazorla's first training session with the team on their Twitter account, noting that the midfielder "returned to where he belonged."
The former Spain international, who has not played since October 2016, said earlier this year that he was hopeful of returning to action in 2019.
Former Arsenal coach Arsene Wenger described Cazorla's injury in November as "the worst I have known."