Porto goalkeeper Iker Casillas suffered a heart attack during training on Wednesday but is recovering in hospital, the club have confirmed.
Reports emerged that Casillas had been hospitalised after falling ill but Porto said his heart problem has been "resolved".
"Iker Casillas suffered an acute myocardial infarction during Wednesday morning training session held at the PortoGaia Training and Training Center in Olival," a statement from the club read.
"Training was promptly interrupted to provide assistance to the Porto goalkeeper, who is currently at the Hospital CUF Porto. Casillas is well, stable and his heart problem resolved."
Messages of support for Casillas quickly populated social media in the wake of the news, with former Spain team-mate Carles Puyol writing on Twitter: "Be strong my friend," and ex-Real Madrid colleague Pepe adding: "We love you."
Current Madrid winger Gareth Bale said: "Get well soon my friend."
Casillas was widely regarded among the world's best goalkeepers during his 16 seasons playing for Real Madrid, with whom he won five LaLiga titles and three Champions Leagues.
The 37-year-old was also in goal for Spain when they won the 2010 World Cup, as well as their triumphs at Euro 2008 and 2012. He won 167 caps in total.
Casillas joined Porto in 2015 and helped them win the Primeira Liga in the 2017-18 campaign.