Ryan Gauld has admitted that the £48m release clause written into his contract at Sporting Lisbon is "a little bit unbelievable" but the teenager is determined to be a success at the Portuguese giants.

Gauld returned to Scotland yesterday having agreed a six-year contract with Sporting to complete a £2.2m move from Dundee United.

The midfielder - who was dubbed Mini Messi at Tannadice - did not need to be sold on a move to Portugal since he had long held an ambition of playing on the continent. Sporting are convinced of the merits of the move too, with officials appended a €60m buy-out clause to his contract.

With the details confirmed, the Scotland Under-21 internationalist flew back into the Edinburgh Airport yesterday. He has been instructed to return to Lisbon within the next few days to begin preparing for the new Primeira Liga campaign. Sporting will also compete in the Champions League next season.

It is the chance to play in a new environment which most appeals to Gauld, although he is not ignorant of the sums of money involved in the deal either. "They've paid a big price but hopefully I can put in big performances for them and establish myself and do well," he said.

"It's a bit unbelievable [about the release clause] just now but hopefully in a few years I can live up to that price tag. I'm just going to have to get my head down and work as hard as I can. I've got a lot in my game to improve on, hopefully I can go there, work hard and see what I can do. It will be hard to leave home and learn a new language but I'm really looking forward to it, it's going to be a good challenge for myself.

"When I first heard of the interest from the manager at United, Jackie McNamara, I was kind of overwhelmed. [But] since I was young I've always wanted to play abroad so hopefully it will live up to what I'm expecting."

The 18-year-old has caught sight of the grandeur at Sporting already, the news of his signing having appeared on the club's official website alongside an image of Gauld posing next to pictures of Luis Figo and Cristiano Ronaldo. Both players started their careers at Estadio Jose Alvalade.

"They're two very good players but I'm just concentrating on myself," said Gauld, when asked about the idea of following in the footsteps of the Portuguese icons. "Everyone knows it's a great club, a very big club, good at developing younger players. That's played a big part in my signing."

He leaves behind a club at which he had become pivotal, playing 38 times for United last season having made his first-team debut at the age of 18. However, the midfielder is confident that he will be given time to settle in at his new club.

"They're looking forward to me going over for training and we'll see how it goes," he said. "The deal shows they're not expecting too much, too soon; it's a long-term investment."