Casillas, 32, has fallen out of favour this season at Real Madrid, making only a handful of appearances since Diego Lopez was made the club's first choice shot-stopper, and it has raised questions about his suitability to be Spain's No.1 with Victor Valdes, Pepe Reina and David de Gea waiting in the wings.
Busquets, who is currently on international duty with Casillas as they continue preparations for the World Cup in Brazil next year with a visit to Johannesburg, South Africa on Tuesday, says he has never seen the Madrid 'keeper work so hard.
“I see him as a little better. It is clear that perhaps he is hoping for a regular place in the team and currently he is not getting that,” Busquets told Marca.
“Now he is working harder in training. He has always worked hard, but now even more so.
“Sooner or later he will get what he wants and we will all be happy, both collectively and personally.”
Casillas has been capped for Spain 151 times and currently holds the record for most appearances, beating former Barcelona shot-stopper Andoni Zubizarreta's milestone back in November 2011.
Meanwhile, Busquets proceeded to hit back at reports questioning the Catalans' playing style following the appointment of Gerardo Martino in the summer, claiming the criticism of the team is unfair.
He added: “We [Barcelona] aren’t at the level we were at during the [former manager Pep] Guardiola era, I don’t think that form is repeatable. But the criticisms Barca get are disproportionate.”