In his interview with Fox News, Witkoff said: "This peace deal is about these so-called five territories. But there's so much more to it… I think we might be on the verge of something that would be very important for the world at large."
"On top of that, I believe there's a possibility to reshape the Russian-United States relationship through some very compelling commercial opportunities that I think give real stability to the region too," he added.
The US and Russia have been holding talks aimed at restoring diplomatic relations.
Zelensky's intervention is not the first time he has criticised Witkoff.
In March, he said: "He doesn't look like a military man. He doesn't look like a general, and he doesn't have such experience. As far as I know, he is very good at selling and buying real estate. And this is a little different."
The Ukrainian leader's comments came after top US, Ukrainian and European diplomats met in Paris to discuss the war - a group that included Witkoff and US Secretary of State Marco Rubio.
Meanwhile Donald Trump renewed his own criticisms of Zelensky on Thursday. He appeared to row back on earlier comments accusing the Ukrainian leader of starting the war but said he was "not a big fan".
"I don't hold Zelensky responsible but I'm not exactly thrilled with the fact that that war started," Trump said.
"I'm not blaming him, but what I am saying is that I wouldn't say he's done the greatest job, OK? I am not a big fan."
Zelensky also told journalists that he had "information" China was supplying weapons to Russia.
"We have finally received information that China is supplying weapons to the Russian Federation," he said.
"We believe that Chinese representatives are engaged in the production of some weapons on Russian territory," he added.
China has not yet responded but has previously portrayed itself as a neutral party in the war.
Beijing did respond to an assertion last week by Zelensky that Chinese nationals were fighting for Russia by advising "relevant parties to correctly and soberly understand China's role and not to make irresponsible remarks".