Iker Casillas has sparked a huge reaction on social media after sharing a video that takes several digs at his former Real Madrid teammate Cristiano Ronaldo.

The legendary goalkeeper reposted a video that compares Ronaldo's career ambitions with the achievements of Lionel Messi, using clips from the Portuguese superstar's own interviews to highlight areas where his long-time rival has surpassed him.

Casillas and Ronaldo spent six seasons together at Real Madrid, winning multiple major trophies during one of the most successful periods in the club's history.

But the former Spain captain's decision to share the video has inevitably reignited the debate surrounding two of football's greatest-ever players.

What Did the Viral Video Say About Cristiano Ronaldo?

The video focuses heavily on comments Ronaldo has made throughout his career about the trophies and achievements he wanted to win.

One clip features Ronaldo explaining that he values winning the European Golden Shoe highly because the award is based on goals rather than votes.

The video then cuts to Messi's six European Golden Shoes compared with Ronaldo's four.

It then moves onto another of Ronaldo's biggest ambitions — winning the FIFA World Cup.

Ronaldo has spoken throughout his career about wanting to lift the trophy with Portugal, but the video contrasts that ambition with Messi's triumph at the 2022 World Cup in Qatar.

The final major comparison focuses on the Ballon d'Or.

Ronaldo has previously spoken about wanting to become the player with the most Ballon d'Or awards in history.

Messi currently holds that record with eight, compared with Ronaldo's five.

How the Video Reignited the Lionel Messi vs Cristiano Ronaldo Debate

The video is essentially built around one of football's greatest debates.

Messi and Ronaldo dominated the individual awards and biggest stages of world football for more than a decade, constantly being compared against one another.

Their rivalry produced some extraordinary numbers.

Between them, they won the Ballon d'Or 13 times, with Messi claiming eight and Ronaldo five.

Messi also eventually achieved the one major international honour that had eluded both players for much of their careers when Argentina won the 2022 World Cup.

Ronaldo, meanwhile, was part of Portugal's European Championship-winning squad in 2016 and two UEFA Nations League titles.

That makes any comparison between the pair almost impossible to settle.

Why the Video Compares Ronaldo's Saudi Move With Messi's Career

Another section of the video compares Ronaldo's move to Saudi Arabia with Messi's career in the United States.

It includes a clip of Barcelona legend Xavi describing Messi as the best player in the world, followed by Ronaldo dismissing the assessment in part because Messi was playing in the United States at the time.

The video then cuts to Ronaldo's own move to Al Nassr in Saudi Arabia.

It finishes with another clip of Ronaldo declaring himself the best player in history, before showing Messi scoring while Ronaldo is involved in the defensive action.

It is clearly designed to provoke a reaction.

And Casillas' decision to repost it has done exactly that.

Casillas and Ronaldo's Six Seasons Together at Real Madrid

The reaction is particularly notable because Casillas and Ronaldo were not simply former players at the same club.

They were teammates during one of the most important periods in Real Madrid's modern history.

Ronaldo joined Madrid in 2009, while Casillas had already established himself as the club's first-choice goalkeeper and captain.

The pair shared the dressing room until Casillas left the Bernabeu for Porto in 2015.

During those six seasons, they won La Liga, the Copa del Rey, the Spanish Super Cup, the UEFA Champions League and the FIFA Club World Cup, among other honours.

They were also part of the Madrid side that finally ended the club's long wait for a tenth European Cup in 2014.

Why Iker Casillas' Repost Has Caused Such a Reaction

Casillas' reputation and history with Ronaldo make the repost more significant than it might otherwise have been.

The former goalkeeper is one of the most decorated players in Spanish football history and was a hugely influential figure at Los Blancos.

He shared six seasons with Ronaldo at Real Madrid and knows him from their time together at the club.

That is why fans have immediately focused on the fact that he chose to share a video that is so openly critical of Ronaldo.

However, a repost does not necessarily mean Casillas agrees with every claim made in the video.

The former goalkeeper has not publicly stated that he believes Messi is better than Ronaldo in response to the video, nor has he directly criticised his former teammate alongside the repost.

For now, the social media activity is what has caught people's attention.

Casillas and Ronaldo's Real Madrid Relationship

Their relationship at Real Madrid was not without its complications.

Casillas eventually left the club in 2015 after a difficult final period at the Bernabeu, with his departure coming amid a turbulent period surrounding the club.

Since retiring, both players have largely followed separate paths.

Ronaldo has continued his career in Saudi Arabia with Al Nassr and remains a major figure for Portugal.

Casillas, meanwhile, has remained involved in football and regularly attracts attention whenever he posts about the sport on social media.

That makes his latest activity particularly likely to generate discussion.

Why the Ronaldo vs Messi Debate Continues

Perhaps the biggest takeaway from Casillas' post is that the Ronaldo-Messi debate remains as powerful as ever.

Even after both players have moved beyond the peak of their careers, their achievements continue to be compared.

Messi has the World Cup and the greater number of Ballon d'Or awards.

Ronaldo has his own extraordinary list of records, including his Champions League scoring record and an international goalscoring record that has made him one of the most prolific players in football history.

Both have built careers that are almost impossible to replicate.

And after more than a decade of arguments between their respective fanbases, it appears the debate is still capable of generating headlines.

This time, however, it was not another player scoring a goal or winning a trophy that reignited the conversation.

It was a social media repost from one of Ronaldo's former teammates.

Casillas' decision to share the video has once again put the debate in the spotlight.