Ronald Koeman insisted that he was "disrespected" by the fourth official during Barcelona's loss to Granada and was left bemused after being shown a red card.
Barca missed the chance to go top of La Liga after being beaten 2-1 by Granada at Camp Nou on Thursday night.
Lionel Messi opened the scoring only for Darwin Machis and Jorge Molina to complete a second-half turnaround for the visitors, with Koeman forced to watch the last portion of the game from the stands after being dismissed by match referee Pablo Gonzalez.
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Machis drew Granada level with a cool finish in the 63rd minute of the game, with the initial move having started from deep in their own half after Antonine Griezmann gave away a free kick.
Koeman was seen protesting to the fourth official following the goal, and Gonzalez ran from the far side of the pitch to show the Dutchman a red card after consulting with his colleague via his earpiece.
What's been said?
Koeman pleaded his innocence post-match while pointing the finger at the fourth official for his role in the incident.
"I don't get it at all. I didn't say anything, I didn't insult him. I spoke to the fourth referee and he disrespected me," said the Barca boss at his post-game press conference.
"I was not wrong, because according to the referee report I disrespected the fourth referee and for me, it is not like that. A lack of respect is insulting.
"I haven't used ugly words, not once. If they're going to put things I haven't said I'll have to do something. I don't understand."
Asked to assess his team's latest performance, Koeman added: "We have to accept that we lost today. It is really tough because it was a good opportunity to win tonight.
"The defeat was mainly due to a lack of concentration in defence during Granada's two goals.
"It is a very disappointing result. It is a very hard defeat because we controlled our own destiny, but we still have five games left."
The state of play in La Liga
Barcelona stayed third in the Spanish top-flight standings after suffering their sixth defeat of the 2020-21 campaign, just behind arch-rivals Real Madrid due to their inferior head-to-head record.
Atletico Madrid are still sitting top by two points with only five games left to play, including a crucial clash against Barca at Camp Nou on May 8.
Koeman admitted his players were frustrated in the dressing room following their surprise loss to Granada, but also stressed the importance of getting back on track quickly away at Valencia this Sunday.
"I spoke to several players after the game. They are very disappointed," he said. "It is very important to win again, because Sunday's game is crucial for our aspirations to win the championship.
"We have to learn from what we have done wrong, we have to put energy into it, improve things and move on.
"There is still a lot at stake and the level has to be very high."