According to Reuters, Moonves is planning to seek autonomy from the Redstone family, the broadcaster's controlling shareholder, in leading the company if it merges with Viacom.
"Shari [Redstone] has to come to understand that if she wants Les, and she does want Les, and Sumner [Redstone] feels comfortable with Les … why not five years?" the chairman and CEO of Gabelli Asset Management said in an interview with "Closing Bell."
While the Redstones have called for the two companies to reunite, negotiations between Moonves and National Amusements (NAI) haven't started in earnest, Reuters reported. The Redstones own an 80 percent stake of CBS and Viacom through NAI.
Gabelli said Sumner Redstone and NAI have to be a "cheerleader for Les."
Meanwhile, he's still bullish on CBS and Viacom, and isn't concerned about the media business in general.
"CBS is a loaded laggard. Viacom is a wonderful opportunity in the sense of distribution in … India. Paramount has great distribution," he said.
— Reuters contributed to this report.