Atletico Madrid midfielder Saul Niguez said he risked his health by playing for two years with a severe kidney problem which meant he "p---ed blood" in every game and training session.
Saul, 22, was hospitalised in February 2015 after receiving an accidental kick in the stomach from Bayer Leverkusen defender Kyriakos Papadopoulos.
He suffered kidney trauma with internal bleeding as a result and was sidelined for 39 days before seeming to make a full recovery and playing regularly for Atletico from then on.
However, Saul told Antena 3 that going back to play at Leverkusen in this season's Champions League round of 16 had brought back memories of how difficult it had been to recover from the problem.
"For two years I was playing with a catheter inside [tube to empty the bladder]," Saul said. "In every training session and every game I p---ed blood. It was pretty bad, something difficult that people do not know or understand. I was risking my health to put on the club colours, to chase the dream.
"I remember everything about the injury -- how I felt, how many times I vomited, being on the stretcher. Scoring the goal back there [against Leverkusen] was a huge liberation and emotion for me. I felt like a weight had been lifted off me. "
The Spain under-21 captain has been linked with a number of Europe's top clubs in recent years, including Manchester United, Barcelona and Bayern Munich, but says that he feels happy at Atletico and still has plenty to improve upon.
"I felt these values in my first year at Atletico," he said. "When you are so young you must take them in, and once you have them you do not want to go anywhere else. You feel comfortable and happy with the people around you.
"I have improved a lot but I would like to improve more, to be better defensively and understand the play better. Sometimes you lose the head a bit, and lose your position, when you should be more relaxed and hold your position, which is better for the team."
Meanwhile, Atletico's travelling squad for Tuesday's Champions League quarterfinal first leg at Leicester includes both forward Kevin Gameiro and backup goalkeeper Miguel Angel Moya, who have been missing in recent weeks due to injury.
"Kevin Gameiro and Miguel Angel Moya have been given the all-clear by the club's medical services after today's training," a club statement read. "The players worked out at the same pace as their teammates and are available for [coach Diego] Simeone for this Tuesday's match against Leicester City."