West Ham United midfielder Felipe Anderson is expected to join Porto on a season-long loan deal on Tuesday.
Although the transfer window closed for English clubs signing players from abroad on Monday, the window in Portugal is open until 25 October.
Brazil international Anderson joined the Hammers from Lazio for £36m in 2018 - a club record fee at the time.
But the 27-year-old is yet to start a Premier League game this season and is one of the club's highest earners.
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Anderson was described by West Ham as "one of the most exciting talents in Europe" when he arrived on a four-year deal, and he has 12 goals and 12 assists in 72 appearances for the club.
However, his only starts in 2020-21 have come in the Carabao Cup. Anderson made substitute appearances league defeats by Newcastle United and Arsenal and was an unused substitute in the wins over Wolverhampton Wanderers and Leicester City.
Although the Portuguese transfer window does not close until later in October, clubs must submit their European squads to governing body Uefa by 23:00 BST on Tuesday.
It means Porto must complete the deal by then if Anderson is to be eligible to play in the Champions League.
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