The teen left Barca this summer after Chelsea met the buyout clause in his contract.
Guiu said, “It was not an issue with my contract.
“I’ve always dreamt of playing in the Premier League and Chelsea is a great club with a lot of history.
“It was a tough decision but it was an amazing opportunity, so I had to go for it.”
Guiu continued: “I’m just focused on the pre-season tour, doing my best and that’s what I can say.
"But (Chelsea head coach Enzo) Maresca told me there was an amazing sporting project full of young talent, that he wanted me to be a part of it and that he had a lot of faith in me and my skills and capabilities.
“I think I’m ready. We work very hard every day both on and off the pitch, on the physical aspect and the practical. So I think I’m ready to be on the pitch and help the team when I’m needed.”