While a number of transfer rumours have linked United with midfielders, Robson believes that they must prioritise defensive reinforcements.
He told The Mirror: "When I look at us, I just think losing Nemanja and Rio and conceding goals last year means can we get a really good centre-half? I think that's more important than a central midfield player at this moment in time.
"When you look back, we've nearly always had a really dominant player who is brilliant in the air and an organiser. If you go back, we've had Rio, Nemanja, Steve Bruce, Gary Pallister and Jaap Stam.
"We've always had a centre-half who is as good as any player aerially, talks to people and is a leader. I feel we need that type of centre-half to improve the team. I can definitely see another couple of players coming into the club."