Sources have told ESPN that Barca had been interested in signing the 17-year-old right-back, but their offer of €10m was not deemed acceptable.
Couto and his agent Marcelo Robalinho travelled to Manchester on Wednesday and the deal will be confirmed once he passes his medical. He will then return to Coritba, where he will remain until he turns 18 on June 3.
As well as his domestic performances for Coritiba, Couto caught the eyes of Europe's biggest clubs for his involvement in Brazil's successful under-17 World Cup in 2019.
He only missed two matches throughout the tournament on home soil -- both through suspension -- and he provided the assist for Lazaro Vinicius to score a stoppage-time winner in the final to secure a 2-1 victory over Mexico.