The 20-year-old Brazilian has already scored for Liverpool, in his home debut against Swansea City.
However, Coutinho admits that he must improve physically and adapt to the pace of the English game.
"I need to improve my muscles because they are still quite small at the moment," he told The Telegraph.
"The difference I've noticed already is you have to be a quick thinker and move around the pitch much sooner because the pace is so much higher.
"It's quite different to what I'm used to but I'm doing my best. I always knew the type of football here would be much harder but with the help of manager, staff and players I will try to adapt as quickly as possible."
Liverpool's next match is away at Wigan Athletic this evening.