The 21-year-old has been sent on loan to Hertha Berlin for the season after falling out with Mikel Arteta.
Speaking in an interview with Canal+, Landreau said: "He annoyed me terribly, he is very complicated to manage," Landreau said.
"He sometimes has some behaviours within a group that are very, very hard.
"But somehow, that's what he is: big; he doesn't let go, he is a fighter. He has an oversized ego, but he certainly needs it."
Asked about Guendouzi's future, Landreau added: It's also what's at stake in his career: how he will manage what he is in order to succeed, or not, in an exceptional career.
"I think he needs to be in the spotlight, to be a leader. He needs to be a captain or vice-captain, and he will try to make the most of it.
"Because that's the way he is. And that means that his teammates have to accept him the way he is, because he's a pain on a daily basis.
"He's very annoying on a daily basis, but on the other hand, he's talented."