By SABC Sport
1st July 2023
Moreira, 18, joined Benfica from Standard Liege in 2020 and was part of the side which won the 2022 UEFA Youth League.
Having made his senior debut in May 2022, Moreira featured regularly for Benfica B last season.
The teenage winger is part of Portugals squad at the European Under-21 Championship, where they will face England in the quarter-finals on Sunday.
Moreiras arrival on a free transfer follows on from the signings of forwards Nicolas Jackson from Villarreal and Christopher Nkunku from RB Leipzig, while Ruben Loftus-Cheek has completed a permanent move to AC Milan.
Loftus-Cheeks departure is one of several recent outgoings as new Blues boss Mauricio Pochettino reshapes his squad ahead of the start of the season.
Arsenal completed the signing of midfielder Kai Havertz, while NGolo Kante, Kalidou Koulibaly and goalkeeper Edouard Mendy all headed for Saudi Arabia.
According to reports midfielder Mason Mount is also set to depart after Manchester United agreed to sign the England international for an initial £55 million.