Herrera spoke about the on-off transfer this morning.
"At no point did me or my agent come to any agreement with United," he said.
"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.
"There are questions United must answer," he added.
For the big stories and the banter follow us on Twitter: @tribalfootball