Mourinho said this ahead of Croatia’s Euro 2020 opener against England on Sunday.
Since leaving Dinamo Zagreb in 2013, Kovacic has played for three clubs, Inter Milan, Real Madrid and Chelsea, all previously managed by Mourinho.
But the 27-year-old has never worked with the Portuguese gaffer.
“Kovacic, I always feel he’s much better than what people think,” said Mourinho on talkSPORT.
“And I am very upset with him because he played in every club I have been to, but never with me!
“He played for Real Madrid, but not with me. He played for Chelsea, but not with me. He played for Inter, but not with me.
“So I love the guy and the guy who followed my clubs… maybe he goes to Tottenham! Maybe he will go to Tottenham next season! But he never played for me.”
“I think England is going to face probably one of the best midfielders in the tournament,” Mourinho added.
“[Marcelo] Brozovic, [Luka] Modric, Kovacic for me is top of the tops.
“Brozovic in England we don’t know so well, fantastic player, very aggressive, great positioning, but at the same time good technique, good arrival in the box even coming from a more defensive position. Modric, we don’t need to say anything.”
