Vicente Navarro collapsed during Valencia's open training session at the Estadio de Mestalla to present new signing Enzo Perez to the club's fans and the 47-year-old was promptly taken to hospital.
Valencia confirmed on their website that Navarro, who is nicknamed 'Serreta', had suffered a stroke but had progressed "favourably" at the hospital Arnau de Vilanova.
"The kit man Vicente Navarro 'Serreta' has suffered [a stroke] during training on Friday whereby, after being treated with urgency on the same turf, has been taken to hospital Arnau de Vilanova, where he remains admitted to observation and the first hours has evolved favourably," the statement read.
According to reports, fans at one end of the stadium alerted Valencia's medical staff to the prone Navarro.
They treated Navarro, which ensured the kit man was conscious when he arrived at hospital.
Friday's training session marked the official return to action for Valencia ahead of La Liga's resumption on Saturday.
Valencia face leaders Real Madrid at the Mestalla on Sunday and Perez, who has joined Nuno's side from Benfica, was bullish about his new team's chances.
"I'd like to make my debut, of course. I'm ready to play," he said before the session began.
"It would be great to make my debut against Real Madrid. And if the goals come, even better. But the important thing isn't scoring, it's that the team wins."
When asked directly if Valencia could defeat Real, Perez said: "Of course. It’s 11 against 11."
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