Asked how Cusack handled his success, Piven tells the February issue of Best Life magazine, "No comment. I mean, you could fill in the blank, I bet."
However, Cusack says in a statement to PEOPLE: "It's quite the contrary. I am very happy for Jeremy. I wish him the best and I always have."
Cusack studied acting at Chicago's Piven Theatre Workshop, which was run by Piven's parents, according to the magazine. And Piven, 41, played wingman to Cusack, 40, in films including Say Anything, Grosse Pointe Blank and Runaway Jury – until he landed the part of Ari Gold on HBO's Entourage, for which he won an Emmy last year.