Barcelona academy product Guiu made his professional debut last October, announcing his arrival with his first goal after just 33 seconds, a late winner against Athletic Bilbao.

He made seven first-team appearances and scored his first Champions League goal in the group stage against Royal Antwerp.

He was Spain's joint-top scorer at the European under-17 Championship last summer with four strikes.

"It's an immense joy to sign for Chelsea and I struggled to sleep ahead of the journey here because I was so excited," Guiu said.

"Ever since I was small, it was my dream to play in the Premier League. Now I have the opportunity to come here to Chelsea and I will work my hardest to be successful for the club."