Hugo Viana has left his role as sporting director of Sporting CP, the Portuguese club announced on Tuesday.
Viana, who will replace the outgoing Txiki Begiristain as Manchester City's director of football, was due to leave Sporting CP at the end of the season.
"Sporting CP informs that Hugo Viana requested that his departure from the Club be brought forward, initially scheduled for the end of the current sporting season," a club statement said.
"Taking into account the arguments presented and by mutual understanding, the sporting director of Sporting CP ceased his duties after the closure of the winter market."
Viana, 42, spent time at Sporting, Newcastle United and Valencia as a player and won 29 caps for Portugal between 2001 and 2012.
He was appointed as Sporting's director of football in 2018 and helped the club win the Portuguese title in 2021 and 2024 despite strong competition from Benfica and FC Porto.
He is credited with bringing in now-Manchester United boss Ruben Amorim as manager in 2020, who also played a key role in returning Sporting to the top of Portuguese football.
"Hugo Viana played a fundamental role in the club's sporting growth during a period in which Sporting CP's main football team won several titles: two National Championships, three League Cups, a Super Cup and a Portuguese Cup," the statement said.
Sporting CP president Frederico Varandas praised Viana and said: "Viana's work over these years was fundamental to the implementation of a solid and winning sporting project.
"He played a crucial role in building a team that broke barriers and marked one of the most memorable phases in the recent history of our Club."
Bernardo Palmeiro will replace Viana as new general director of football at Sporting.
City, meanwhile, had a busy January transfer window.
Pep Guardiola's side spent £180 million ($225m) in an attempt to spark their season into life after a dismal first half of the campaign.
City brought in Eintracht Frankfurt's Omar Marmoush in a £59m transfer, followed by Palmeiras' Vitor Reis for £29.6m and Lens' Abdukodir Khusanov for £33.6m.
Before Monday's deadline, City secured the arrival of FC Porto's Nico Gonzalez by splashing £50m, equivalent to the player's release clause.