"He's created a monster in advertising, he's created a success story that is very difficult to replicate," Sawiris, a billionaire who made his fortune building a telecommunications empire from the Middle East to South Asia, told CNBC's Capital Connection.
Sorrell is "a workaholic" who knows all his numbers and subsidiaries, said Sawiris, who owns a telecom company in North Korea and also has business interests in gold mining. "This is not the kind of guy you can replace and think the next CEO will do a good job."
Sorrell, credited for turning WPP into the world's biggest advertising agency, quit on Saturday amid allegations of personal misconduct. In a statement, the 73 year-old businessman said, "WPP is not just a matter of life or death, it was, is and will be more important than that."
Chairman Roberto Quarta will take on the role of executive chairman until a new CEO is found.
"I hope that his legacy doesn't fall by this disruption," Sawiris said, adding that he believed WPP should consult Sorrell on choosing the next CEO. If a successor is chosen abruptly, that could be "very dangerous," the Egyptian billionaire cautioned.
During his three decades in the industry, Sorrell developed a reputation for strong opinions and an autocratic management style.