The 17-year-old is believed to be on the radar of a number of European clubs, with Arsenal and Bayer Leverkusen both recently credited with an interest in the Brazil Under-17 international.
However, according to Globoesporte, the Spanish champions have concluded a deal for the right-back, who will arrive at Camp Nou once he turns 18 on June 3.
The report claims that the Catalan giants will pay an initial £4.6m for the teenager, although the transfer fee is expected to rise with various add-ons.
Couto is yet to make his first-team debut for Coritiba but has impressed for their Under-20 side.
Barca suffered their fourth La Liga defeat of the 2019-20 campaign on Saturday afternoon as Valencia recorded a 2-0 win at the Mestalla.