The Old Trafford outfit had a bid for the midfielder rejected last week and the playmaker's dad revealed any move to David Moyes's side would be hard to tricky
The Basque club confirmed on Friday that they had received an offer from the Red Devils for their 24-year-old playmaker, while Goal understands the Liga club rejected a €30 million offer.
Reports suggested it would take a bid of €36m (£30.75m) to prise Herrera from the Spanish outfit and his father believes it will be hard for him to move to Old Trafford.
Speaking to Mundo Deportivo, Pedro said: "Ander is getting on very well at Athletic, very content. He's fought hard to come to this club and it's very difficult for him to leave.
"I think it's Manchester United's decision, since they have not found a replacement for Cesc Fabregas. They've decided to opt for a creative player and have thought about Ander."
United manager David Moyes said in his Friday press conference that he expected the club to be “very busy” in the final days of the transfer window.