Gandolfini died Wednesday in Italy of a suspected heart attack. He was 51.
Gandolfini "was a genius. Anyone who saw him even in the smallest of his performances knows that," Chase told TMZ.
"He is one of the greatest actors of this or any time. A great deal of that genius resided in those sad eyes. I remember telling him many times: 'You don't get it. You're like Mozart.' There would be silence at the other end of the phone.
Chase went on to offer his heartfelt condolences to Gandolfini's wife and two children.
"For Deborah and Michael and Liliana this is crushing," the writer-producer said. "And it's bad for the rest of the world. He wasn't easy sometimes. But he was my partner. He was my brother in ways I can't explain and never will be able to explain."
Steve Carell, Gandolfini's co-star in the 2013 big-screen comedy "The Incredible Burt Wonderstone," expressed his sadness via Twitter.
"James Gandolfini. Unbelievably sad news. A fine man," Carell tweeted.
"Mary Pat & I express our deepest sympathies to Mr. Gandolfini's wife & children, and our prayers are with them at this terrible time," Christie said. "I have gotten to know Jimmy & many of the other actors in the Sopranos cast & I can say that each of them are an individual NJ treasure. ... I was a huge fan of his and the character he played so authentically, Tony Soprano. ... James Gandolfini's passing is an awful shock. He was a fine actor, a Rutgers alum and a true Jersey guy."