Coutinho visited the Hospital of Barcelona early on Monday to complete the first part of his medical and is due to undergo final checks at Camp Nou later.
He will then meet some of his new team-mates before finally signing a five-and-a-half-year contract, alongside club president Josep Maria Bartomeu. He will then be officially presented to the media and fans.
The 25-year-old will pose with the Barca shirt but he has not yet been assigned a new squad number, according to the Catalan press.
It has been suggested he will take number 22 if Aleix Vidal moves to Sevilla on loan, as expected.