"Sometimes the best answer is to be quiet," those were the words of Real Madrid striker Cristiano Ronaldo in his reaction to tax evasion accusation.

He is being accused of evading paying taxes worth 14.7 million euros ($16.4 million).

The Portuguese star forward wrote on Instagram, with a photo of himself in a Portugal polo shirt and right forefinger raised to his lips - "Sometimes the best answer it's to be quiet."

Ronaldo insisted Wednesday that he had a "conscience clear, always", as he arrived at Lisbon airport to fly out to the Confederations Cup in Russia.

Real Madrid have given their backing to Ronaldo, saying they had "full confidence in our player Cristiano Ronaldo, who we understand has acted in accordance with the legality regarding the fulfillment of his fiscal obligations".

32-year-old Ronaldo; the world's highest paid athlete according to Forbes magazine, follows in the footsteps of Barcelona forward and Argentina star Lionel Messi, who was found guilty of the same offence last year, although the sums involved were allegedly smaller.

If he too is put on trial and found guilty, he risks "a fine of at least 28 million" euros and could potentially be jailed for three-and-a-half years, according to the Gestha union of experts at Spain's Inland Revenue.