Koeman is a former club legend and the new manager of the Catalan club.
“I can tell you about Koeman from my personal experience, and I have very little to tell you about Koeman,” he told local radio.
“He provided me absolutely nothing. I wasn’t happy, I asked to leave and I went to AC Milan. We’ll see how he does at the Camp Nou,” the Watford winger said.
Barcelona are looking to Koeman to help them turn the page after a disaster of a campaign under two different managers.
“The truth is that Barcelona’s [situation] does not bother me,” Deulofeu said.
“In fact, right now, I don’t care.”
The forward was seen as a highly rated prospect when he came in through the youth ranks. But he never broke through to the first team.
“At Barcelona, they have not had patience with La Masia for years. If you give [the youngsters] time, they learn the style of the first team. There are players, many of us have come from there, but not patience. Now there will be changes, but they are years behind,” Deulofeu said.