Koeman is fighting to keep his job after last night's disappointing 1-1 draw with Granada at the Nou Camp.
"Barcelona is in a difficult moment," said De Boer. "It is sad, but now we have to think about what to do. With calm, that is the most important thing. We have to look at what is not going well.
"There are new players and you have to be patient. Koeman has to continue."
De Boer continued: "I have the feeling that he is a very good coach, he has a Barca heart and will surely be successful in the coming seasons."
Asked if the media are being unfair towards Koeman, De Boer added: "I think so. The media have to lead, each person has their opinion, it is difficult at this time. It is the life of a coach. I hope the president has peace of mind."
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