The move eventually fell through due to United's unwillingness to pay his £30m release clause, but the 24-year-old has instead insisted that he had no contact with the Premier League champions.
"I feel very flattered to see that one of the biggest clubs in the world made an offer for me," said the Spaniard. "At no moment did either I or my agent reach an agreement with United. At no moment did I speak with United.
"I do not know if they spoke with my agent, but after that they would need to persuade me [to leave Athletic]. They had to pay the clause and then make a more persuasive case to me than Athletic. I never saw myself elsewhere."
The proposed transfer was also shrouded in mystery on Monday evening when lawyers attended the La Liga offices in Madrid, having claimed that they were there to act on United's behalf - a claim that the Red Devils have since denied.
However, Herrera believes that United should clear up the situation: "The lawyers who were at the LFP offices did not represent me. I did not even know who they were. There are questions which United must answer," he added.
Reports have claimed that United may return for Herrera during the January transfer window.