Jurgen Klopp believes Romelu Lukaku has matured at Manchester United, although he never doubted his "world class" ability.
Lukaku joined United for a reported £75million ahead of the Premier League season and has made a stunning start to life at Old Trafford, scoring 11 goals in 10 games in all competitions.
Klopp's Liverpool welcome Lukaku and United to Anfield on Saturday and the Reds boss hailed the forward's development since making his big move.
"He has matured, of course," Klopp told a pre-match news conference. "He's still a young player. I don't think there was any doubt at any point of his career that he would be a world-class striker - and he was already a world-class striker at Everton.
"Now, being around these other fantastic players at Man United helps him and he has helped the team so far a lot.
"They have been real goal-getter goals. It was: first try? No. Second try? There. And then do it again. It was not always fantastic play, it was fighting for goals.
"He clearly enjoys life in this team a lot. He has all the confidence you need as a striker and I'm sure he's improved since he joined Manchester."
Klopp will be reunited with Henrikh Mkhitaryan - a player of his at Borussia Dortmund - on Saturday and he had praise for the United man, even if he feels he may lack the edge to become an elite star.
"He is a fantastic player, he was always a fantastic player," Klopp said. "We played against him at Shakhtar Donetsk. Wow. He had the perfect attitude.
"But he had the perfect mentality, too. He knew what he wanted to do in each moment of his life. He was the perfect boy, son-in-law, whatever.
"Sometimes, in football, you need to have something a little bit different. We all know some of the best players in the world have a few little issues and that's absolutely okay - they're all human beings."