Chhetri, who will be flying to the Iberian country in another two weeks' time, will be drafted into the club's B side initially. Based on his performance, the club will take a call on whether he should be fast-tracked into the main squad.
"From 163rd (India's FIFA ranking) to playing in the 5th ranked nation in the world, it's one opportunity I will never forget in my life," Chhetri said after the deal was made official, here today.
Chhetri, naturally, is aware that a tough test awaits him in Europe.
"I will have to do a lot of hard work. I will leave no stone unturned, so that I don't regret later in my life. When I am 40, I don't want to feel that I could have done better," he added.
Though the modalities of the deal are yet to be worked out, Chhetri is certainly going to play this season.
"I am excited. I want to see where do I stand...Want to grab it with both hands. I can't let go this opportunity."
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Chhetri is no stranger to Portugal and he has been there a few times on a training-cum-exposure trip as part of the Indian squad.
"The training facilities there are excellent. Now, I feel like a 14-year-old. I will not be Sunil Chhetri there (referring to his popularity in India)."
While Chhetri was naturally over the moon, no less excited was ALL India Football Federation president Praful Patel, who called the development a "beginning of a new era" in Indian football.
"It is truly a very remarkable occasion for Indian football. It's an important milestone. He will be playing shoulder to shoulder with some of the top players of the world. This is a beginning of a new era in Indian football," Patel told reporters.