An iconic figure at Santiago Bernabeu, Casillas has endured a humbling fall from grace at club level.
First dropped to the bench by Jose Mourinho in 2012/13, the Spain international has been unable to dislodge Diego Lopez from the starting XI - with Carlo Ancelotti continuing to overlook him on a regular basis.
A man who has won just about every major honour, including the World Cup with Spain, is reluctant to waste away the years stuck on the bench.
A switch to Manchester City has been mooted, with Joe Hart out of sorts at the Etihad Stadium, while Arsenal have been linked with his services in the past and there would be no shortage of interest from across Europe were he to become available.
Casillas has been reluctant to discuss the issue of his future thus far, but has hinted that an exit could happen at some stage and Balague believes the summer of 2014 could see his 24-year association with Real Madrid brought to an end.
He told Revista de la Liga: "Manchester City definitely want Iker Casillas for next season. He's known about it for a while, but they are not the only team that are after Iker Casillas.
"It will be up to him what he does next, obviously. But if he continues to not play, and he won't unless Diego Lopez gets injured, then he wants to leave Real Madrid at the end of the season.
"He's had enough and he's imagining the possibility of playing abroad. Although he loves the Premier League, maybe it doesn't suit his game as much as the Italian league or the German league.
"But he's going to have offers and if he continues like this, he will leave Real Madrid."
Casillas is one of several goalkeepers to have been linked with a move to City, with the likes of Victor Valdes, Julio Cesar and Asmir Begovic mooted to be on their radar.
Speculation earlier this week claimed that City were preparing a bid to sign Begovic from Stoke in the January transfer window and would send Hart in the opposite direction to ensure the England keeper is ready for the World Cup.
However, speaking ahead of Wednesday night's UEFA Champions League tie against Viktoria Plzen, for which Hart has been recalled, City boss Manuel Pellegrini denied claims he wants to offload England's No.1.
"There is a lot of news about six or seven goalkeepers that we want to buy but it is not true," said the Chilean.
"There is no chance that Joe Hart could go out of this squad in January."
Stoke have also dismissed the rumours and chairman Peter Coates has confirmed there has been no approach from City for Begovic.
Coates told The Sentinel: "This latest story was certainly news to me and I suspect it is just a bit of speculation. That's my guess, anyway, and we have certainly had no approach.
"He is a top goalkeeper, so this kind of thing is going to happen. We are just concerned that he concentrates on playing for us and doing what he has been doing up to now.
"It is important we keep him for the rest of the season. It is an important season and he is a key player. He certainly hasn't made any noises."