West Ham United have completed the signing of Portuguese Under-21 international Mateus Fernandes from Southampton in a deal worth over £40 million, the Premier League club confirmed on Friday.

The 21-year-old midfielder has penned a five-year contract with the Hammers, who are currently bottom of the league after losing their opening two fixtures and suffering an early League Cup exit against Wolves.

“I’m very happy to be here, and I’m very excited to play for West Ham,” Fernandes said after the move was announced. “It’s a big step for me. It’s a big club, a massive club. The project, the stadium, the city, everything. The most important thing is to give everything every day.”

The highly rated midfielder endured a difficult Premier League introduction with Southampton last season as the club suffered relegation, but West Ham believe he has the qualities to strengthen their struggling squad.

Manager Graham Potter expressed confidence in the signing, describing Fernandes as a player of character and potential.

“Mateus is a young player who has made impressive progress in the early part of his career, and we are delighted to have secured his signing,” Potter said. “He gained valuable experience in the Premier League last year with Southampton. His attributes and strengths will bring a different dimension to the squad, and I know he can’t wait to get started here.”

Fernandes could make his debut when West Ham face Nottingham Forest at the City Ground on Sunday, as the club looks to turn around a difficult start to the season.