Athletic Bilbao sporting director Rafael Alkorta has confirmed the club want in returns for Javi Martinez, Ibai Gomez, Ander Herrera and Fernando Llorente.
All four players previously starred at the San Mames with United midfielder Herrera and Tottenham striker Llorente particularly strongly linked in recent months.
Alaves midfielder Ibai – who has also been linked with a move to Leeds United – and Bayern Munich’s Martinez are also reportedly under consideration.
“We are interested in Javi Martinez, Ibai Gomez, Ander Herrera, Fernando Llorente ... we are interested in all of them,” Alkorta told Cadena Ser.
“Any player who can represent Athletic (through their Basque roots) will interest us and players in that quality bracket interest us, so yes.
“We are aware none of these deals would be easy but we are interested in exploring the possibilities of what we can do.
“We have not made any moves yet but we will get to work this week and get going on these fronts.”