The Croatia midfielder has joined Chelsea on a season-long loan.
Modric was at Spurs between 2008-12 and Kovacic said: "I speak to Luka always. He is, of course, happy for me.
"He is sad that I am leaving because we are very close there but he told me that London is an amazing city.
"He said the Premier League will be tough in the beginning but he said it is a nice League, the stadiums are always full and I will enjoy it.
"I am excited to play with him (Jorginho) and I think we will enjoy ourselves together on the pitch. But there is a coach who needs to decide. I need to do my best to prove myself."