The former Red was delighted when Liverpool swooped to sign Coutinho in January.
Warnock told LFC TV: "I think since he's come in, he's adapted well to the game and the style Liverpool want to play.
"I remember seeing him for the first time when he was at Inter Milan and they played Tottenham. It was when Rafa [Benitez] was manager and he played for them a few times in the San Siro.
"I thought he was a very good player and kept my eye on him.
"He seems to be a player the fans like as well and they've taken to him. Scoring quite early on helped him, but he's been impressive."