United ended the season sixth in the Premier League and fans were furious at Old Trafford.
Some vented their fury towards Paul Pogba, who had to address the crowd as tensions threatened to boil over.
Mata, speaking to The National, has admitted that he was shocked by the lap of honour going ahead.
“That just wouldn't happen in Spain at a huge club where expectations are as high as they are at United," he said.
Mata also admitted that he understood the feelings of fans inside the stadium.
“I can understand why the fans felt like at the end of the season," the Spain international added.
“Results were not good and in the last game of the season we lost at home to a team who had been relegated.
“We let people down, we let ourselves go. We lost the chance to compete in the Champions League."
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