The former Brighton manager is favourite for the OM post.
But Rothen told RMC: "There is too much hype about foreign coaches. I struggle to understand De Zerbi: some great experts tell us that he is a fantastic, brilliant coach, who is revolutionising football. I have seen his teams play very often and we cannot say that he is the greatest in Europe.
"Let's put Shakhtar aside because they were forced to leave due to the war. With Sassuolo he did good things but he finished eighth. He didn't impress me when he played at the Vélodrome in the Europa League against OM. In the second leg they won only 1-0, a dominance...
"The experience at Brighton ended in disaster, since February he has won only one match. Forgive me if I have doubts about De Zerbi's real abilities, I can't define him as a great coach."