The 22-year-old midfielder admits that it would be hard to turn down a move to the Premier League outfit but has not been contacted by the Red Devils yet
The 22-year-old has been courted by both the Red Devils and their rivals Liverpool this summer but the player has not been contacted directly from any clubs yet.
"The truth is that so far I know nothing about what is happening, I am not aware,” he told the Raza Deportiva.
"From what I've heard there has been some news, but I have had no approach from the Pachuca club president or the people from Manchester.
"If given the opportunity to emigrate to European football of course I'd go but I have wait to see what the club officials say."
Pachuca chairman Jesus Martinez Patino claimed in May that both Premier League teams had shown interest in the player's signature.
Now, Fassi has revealed that the club have received a written approach from the Red Devils but did not elaborate on how far talks had progressed.
"There is an official interest," Fassi told ESPN. "We have the document [from Manchester United], but there's nothing else to add at this time."
Fassi was keen to keep Herrera at the Estadio Hidalgo but insisted that the Liga MX club would not hold the playmaker back if the right move presented itself, predicting that he would eventually move to England.
"We want him to continue in Pachuca," Fassi added. "We know he's going to emigrate to England, though. Manchester United and Liverpool have talked to us."
"At whatever moment he wants, he can leave Pachuca and the club will give him the opportunity to do so."