The La Liga side confirmed that the Thai star will join them in the next campaign, with Teerasil having undergone a one-month stint at Atletico Madrid last year.
Now, former Singapore striker Noh Alam Shah has stated his belief that the 25-year-old Bangkok native could potentially pave the way for players in the region to make the move to Europe.
"Anyone from Southeast Asia, if they go out of their country to play overseas, will set a standard for other footballers here to follow," he told Goal in an exclusive chat.
"They will believe that everyone, not just Teerasil, can go if they work hard and believe they can."
The Tampines Rovers striker, once feared as one of the best forwards in the region himself, believes Teerasil is unrivalled currently.
"He's an established one and as I've seen him playing, [I feel] he's the number one striker in Asean," he said.
"It's definitely a good thing for him having a chance to play in Spain. Teerasil is such a great player and deserves to play in a great team.
"It (the move) is no surprise to me. He's ahead of everyone. I think he becomes better and better every day."Teerasil has vowed to do his best as he seeks to grab the most of his opportunity to play in Europe.