The Red Devils were shaky at the back last term as they surrendered their crown and finished eighth under David Moyes.
The situation is likely to worsen next season as it stands, with experienced duo Rio Ferdinand and Nemanja Vidic having both left without replacements coming in.
Phil Jones, Jonny Evans and Chris Smalling are currently Louis van Gaal’s options at the back, and with the Dutchman likely to use a three-man unit there is an obvious need for additions.
Bruno Martins Indi, Stefan de Vrij and Mats Hummels have all been linked with moves to Old Trafford, and Robson – who won two Premier League titles and three FA Cups with United – believes that his former side have no chance of topping the pile without top class signings at the back:
“When you lose class defenders like that you need to bring in a really top-drawer centre-half to the club,” he is quoted by talkSPORT.
“That would really give us a chance of winning the title.
“You look back over the years and United have had Brucey [Steve Bruce] and Pally [Gary Pallister] as a pairing, and we’ve had Nemanja and Rio more recently.
“Then we had Jaap Stam. He was a really dominant and aggressive player and we need one of those to come in to the club.”