Bruno Fernandes admits Manchester United will find it hard to replace Edinson Cavani and Paul Pogba.
Cavani will be a free agent in the summer, while Pogba continues to be linked with an exit before his contract expires in 2022.
And Fernandes says both players will be key for United if they want to challenge for bigger honours next season.
"Of course we know they are really important for us, the qualities they have for us are difficult to find on the market for a good price," Fernandes told reporters ahead of the Europa League semi-final against Roma on Thursday.
"I think everyone knows the team is moving up and with their help too so it is important for us that we keep our best players and we keep improving the team."
