Ronald Koeman admits he had to put a rocket up Virgil van Dijk after his move to Southampton.
The centre-back joined from Celtic in 2015 in a £13million deal and quickly established himself as one of the Premier League's best defenders.
A £75million switch to Liverpool followed, with Van Dijk going on to become a key man as Jurgen Klopp's side won the Champions League and the league title.
But the man who took him to England admits there were some issues to iron out after the Dutchman's spell in Scotland.
Koeman told UEFA's official website : "I think it was great to work with Virgil because he was an open guy in (terms of) communication.
"He liked to learn from everybody. He had to change his personality a little bit because sometimes he was a little bit too lazy.
"Maybe people will tell you that he was a little bit arrogant in his football.
"We worked really hard, but the credit is for the player. He is now, in my opinion, one of the best defenders we have in football."
Van Dijk faces missing the rest of this season after suffering a cruciate ligament injury in Saturday's derby with Everton.
