Fandi Ahmad's sons jetted off to the Spanish coastal city of Alicante early on Monday morning, where they will join the academy team of second division club Hercules for three months.
Fandi said that if his sons - Irfan, 15, and Ikhsan, 13 - can adapt to life in Europe, they have the option of signing for three years.
"Irfan and Ikhsan have the talent but over the years they have become more determined as well," said the former Lion before accompanying them on board Qatar Airways flight 639.
"It is not easy to succeed in Europe. There are always so many players on trial. But my boys are mentally tough."
Thirty years ago, Fandi, regarded as one of Singapore's best footballers, signed for Dutch top-flight club Groningen.
He famously scored against Inter Milan in the Uefa Cup that year.