Socceroos legend Tim Cahill's teenage son Kyah has signed an academy deal with Spanish second division club Rayo Vallecano.

The 18-year-old Kyah posted to his Instagram a photo of him signing his new contract with the caption "Same city, new colours".

He'd previously been with fellow Madrid-based club Leganes after joining their youth ranks last year, as he aims to follow in his father's illustrious footsteps.

Cahill, who scored a record 50 goals in 108 appearances for Australia, played in four World Cups and appeared in 600 professional matches at eight clubs all over the globe, swiftly congratulated his son on his switch.

"My man making moves ... Always proud of you, work hard and most importantly have fun," Cahill posted on his Instagram page in reply to Kyah's news.

Kyah isn't the only one of Cahill's children shooting for a career in football with another son Shae and daughter Sienna also starting to forge their paths in English junior systems.

Shae, 15, is in the academy set-up of Premier League club Everton, the club where his father spent eight years playing 278 games.