Icahn’s remarks follow the GOP’s first televised presidential debate Thursday night on Fox News.
Trump reportedly earned the most attention on social media during and after the contest.
Icahn’s tweets Friday are not his first responses to public offers made by Trump.
The billionaire investor initially turned down Trump’s hypothetical cabinet opening during comments made in June.
“I am flattered but do not get up early enough in the morning to accept this opportunity,” Icahn said June 19.
“I was extremely surprised to learn that Donald was running for president and even more surprised that he stated he would make me secretary of Treasury,” he added, denying Trump just three days after the business mogul’s 2016 campaign launch.
Icahn also admitted in June he agrees with Trump that there is a “big fat bubble coming up” in the market.
Years of near-zero interest rates from the Federal Reserve, he argued then, have inflated asset prices.
“I personally believe we are sailing in dangerous, uncharted waters,” Icahn said. “I can only hope we get to shore safely.”
Trump also floated private equity billionaire Henry Kravis and General Electric CEO Jack Welch as potential picks for his cabinet upon entering the 2016 race.
He has since emerged as the leader in polls for the GOP’s presidential nomination next election cycle, despite criticisms of his lack of political experience.
– Updated at 4:03 p.m.