The pair started together in Sunday's 3-1 home defeat to Roma and Mazzola was unimpressed.
"It's evident Cassano cannot play alongside Milito, yet keeping him as a reserve would be an insult to football. We'll see what happens at the end of the season," he told Radio Incontro.
"Inter suffered with the way Roma played. The Giallorossi have started well, just as Zdenek Zeman's teams often do.
"Andrea Stramaccioni is doing well on the Inter bench, but we have to give the team time to get results."