The Reds playmaker, who finished as the club's top scorer with 14 goals across all competitions, had an extended pre-season break because of international commitments, but says he is ready to go for the season.
"I am very happy to be back here and I am ready to start pre-season," Coutinho told the club's website.
"I am working; every day I try to improve and I hope this season I can do even better than the last season," he continued. "I am always aiming to improve.
"It was a good season. Of course, we wanted to win something, but we are ready here to start again to do everything to have a better season.
"Everyone has big confidence and this is the key for the players. I am confident – I think everyone is."