The 33-year-old Argentine spent five years with the Spanish club before a move back to his homeland with Boca Juniors.
"Well, I would go tomorrow," Riquelme told Marca. "I would ask Boca for permission and then I would go.
"Villarreal are also my club. It is part of my life. I have always loved it, they treated me wonderfully and if they need me, I will be there.
"I am sure they will do well anyway, but if they want, I will board a plane and go there."
Villarreal currently sit 17th in the La Liga table.