Former Spain keeper Casillas is in a stable condition after a heart attack during training with Porto.

The 37 year-old – Spain's record appearance maker with 167 caps – was hospitalised but the Portuguese giants confirmed his "heart problem resolved".

After leading Barcelona to a 3-0 win over Liverpool in the Champions League semi-final first leg, two-goal hero Messi sent his well wishes to the former Real Madrid star.

"Happy with the result of tonight," Messi wrote via Instagram post-match. "But we still have to go to Anfield, a very difficult stadium, where Liverpool – who are a great team – will push hard.

"The most important moment of the season is coming and we have to be closer and united than ever.

"Finally I want to take this opportunity to send a hug to Casillas and wish him to recover very soon."

        View this post on Instagram                   Contentos con el resultado de esta noche. Pero aún nos queda ir a Anfield, una cancha muy difícil, donde el Liverpool que es un equipazo apretará mucho. Viene el momento más importante de la temporada y hay que estar más juntos y unidos que nunca. Por último, quiero aprovechar para mandarle un abrazo a @ikercasillas y desearle que se recupere muy pronto. A post shared by Leo Messi (@leomessi) on May 1, 2019 at 3:08pm PDT

Casillas won five LaLiga titles and three Champions Leagues during 16 decorated seasons with Real Madrid, while he was Spain's last line of defence during its golden period – winning Euro 2008 and Euro 2012 either side of the 2010 World Cup. 

He joined Porto in 2015 and helped them win the Primeira Liga in the 2017-18 campaign.

This season, Casillas has made 31 league appearances and 42 in all competitions for Porto – which lost to Liverpool in the Champions League quarter-finals.