The Magpies gained promotion to the Premier League last season and are looking to bolster their squad with the hope of retaining their top-flight status.
But despite owner Mike Ashley pledging to support manager Rafael Benitez and give him "every last penny," the club's only signing this summer has been Christian Atsu for a fee in the region of £6.2m ($8m).
However, according to the Chronicle Live, the Spaniard is now using his contacts in his home country to lure players to Tyneside.
One of those players is Casilla, who was managed by Benitez during the latter's brief stint at the Bernabeu. The 30-year-old joined Madrid from Espanyol in 2015 but has seen his role reserved to being the second choice goalkeeper to Keylor Navas.
With just 15 league appearances in two seasons along with Madrid's everlasting interest in Manchester United's David de Gea, the chances of Casilla getting regular game time are slim.
With Newcastle looking to strengthen in the goalkeeping department, the club is monitoring the Alcover native's current transfer situation.
Casilla is not the only La Liga player the Toon are interested in as they are looking to finalise a deal for Eibar defender Florian Lejeune as well, having been in discussions with the Spanish side for over two weeks.
Newcastle have also made it clear that they are willing to take some of Los Blancos' talented youngsters on loan this season.