Brazilian teenager Luis Guilherme has been confirmed as the first signing of the Julen Lopetegui era at West Ham.

The Hammers will pay an initial £20million plus a potential £6m in add-ons for the winger, who underwent a medical on Tuesday and joins from Palmeiras.

Guilherme, who is considered among the best young talents in Brazil, has agreed a five-year contract with the option of a further year, joining officially on Friday when the summer transfer window opens.

He received late interest from the Saudi Pro League but West Ham moved quickly to wrap up a deal for him, subject to a work permit being issued and international clearance.

“I’m very happy to be signing with West Ham United, a Club that trusted in my work,” said Guilherme. “I also want to thank everyone at West Ham, particularly Tim [Steidten] and his team who came to Brazil, and not only talked with me, but also with my family.

“They presented the project, and both my family and I liked it. So, I'm very happy to be signing with this Club and hope to contribute as much as possible. If things go well, we have a beautiful journey ahead.

“The Head Coach and I already had a conversation. He showed me his project and I believe I’ll learn a lot from him. He’s coached at the national level in Spain and managed big clubs.

“The Premier League is the best league in the world. I believe I’ll improve a lot here with the entire staff at West Ham, which is crucial for my development.

“Growing up, whenever I had the chance, I watched English football. Seeing how it is and now being able to play here is an incredible feeling.

“Since I was eleven, I had this dream, and now it’s becoming a reality. I’m very happy about it and grateful to West Ham. Let’s go for it!”

The 18-year-old’s arrival is expected to kick-start a summer spending spree at West Ham, with their technical director Tim Steidten set to lead a significant overhaul of the first-team squad.

The Hammers are targeting as many as six signings. A centre-forward, right-back and at least one new centre-back are understood to be top of their priorities.

Steidten has been in Brazil for talks over several deals. West Ham were in discussions over a move for Flamengo centre-back Fabricio Bruno but a £15m deal fell through.

West Ham will also be forced to target homegrown talent or else risk falling foul of Premier League regulations, which limit clubs to a maximum of 17 non-qualified players in their squads.