The 24-year-old admits he is flattered by the interest from the Premier League champions but insists he is happy to stay with his current club
The Premier League champions approached the Spanish club with an informal offer below the 24-year-old's €36 million buyout clause, however the bid was rejected.
Herrera, who admits he was flattered by United's interest, also claims that three lawyers - later reported to be 'imposters' - who were seen entering the offices of the Spanish football league [LFP] were not acting on his behalf.
"I reached no agreement with United," he told a press conference. "I knew that United were going to make an offer, but we all know the way the club acts [in these situations]. There are questions United must answer.
"I am proud they made an offer for me, and that Athletic wanted me [to stay]. I do not feel used by United, they made a formal offer. Athletic did not want to negotiate, I value that.
"I feel very flattered to see that one of the biggest clubs in the world like United made an offer for me. The lawyers who were at the LFP offices did not represent me. I do not know who they were.
"I don't discuss hypotheticals. I am just telling you how things were. At no moment did I speak with United. They had to pay the €36m clause and then seduce me more than Athletic. I never saw myself elsewhere."