The 27-year-old has failed to rekindle his Liverpool form following his €160million switch in January 2018, struggling to make an impact during his first full season at the club.
The attacking midfielder managed only five LaLiga goals in 34 appearances last season and failed to nail down a place in the starting XI, with 12 of his league outings coming from the bench.
Coutinho's underwhelming form has seen him become a target for Barca supporters who have jeered him on several occasions, while media reports have linked him with a move.
Speaking after the game, Coutinho admitted that things have not going according to plan during his time in Spain.
Asked by reporters if he had a message for Barca's fans, Coutinho said: "I do not have much to say to them; I am grateful for all the support that I have always received.
"I had a tough time on the field because I have not performed as expected, but football is like that and I'm working hard to improve."
Speaking about his role in Brazil's opening win of the tournament, he added: "It's a very happy day to have scored two goals, to have helped the team and come out with a victory."
Brazil's next Group A game is against Venezuela on Wednesday.