The Portugal international saw a deadline day deal collapse last summer, even after passing a medical.
He told O Jogo: "This story is in the past, but it will of course stay with me for the rest of my career.
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"That episode was like a punch in the stomach, but life goes on.
"I can only work hard so that one day I get a similar chance."
He also said: "I was honest with Marco Silva. I told him what was on my mind. He was also a player and understood me."