De Boer revealed a conversation he had with Bayern Munich coach Pep Guardiola about past personalities.
"Of course I understand why Pep doesn't say that Messi and Neymar can't play together," De Boer told Voetbal International. "He want to keep the relationship with Barcelona good. And of course he hopes that it will work out.
"But in the past, with Samuel Eto'o or Zlatan Ibrahimovic near Messi, Pep himself found out that two leaders doesn't always work. Just like he said to me that two is too much. I understand the doubts.
"It's great to have two players who can score goals. But to put it in the right words: it does not happens often that two star players perfectly work together.
"I'm too far away from the situation to judge about the characteristics of Messi and Neymar. But there will be a moment that one star player thinks he's more important then the other."