Fans bombarded club chief Edward Woodward with messages to bring in Napoli defender Kalidou Koulibaly.
United have interim manager Ole Gunnar Solskjaer in charge which could mean they don’t go in for a signing during the January transfer window.
But supporters don’t want the club to wait until the summer when there may well be a new face at the helm.
Former manager Jose Mourinho wanted reinforcements but the club has been reluctant to spend heavily having made a big investment over recent campaigns.
In particular, supporters have cited the need to boost their defence and see Koulibaly as the right man.
Fans took to Twitter after United announced that youngster Ethan Hamilton would be going out on loan to Rochdale for the remainder of the season.
There were comments like “Koulibaly please”, “this ain’t Koulibaly” and “that’s great and all but I think it’s time to announce a CB”.
Koulibaly wouldn’t come cheaply though and United aren’t the only club around Europe that are looking at him.
Real Madrid are also rumoured to be interested in the player with a £90million price tag.
Woodward and the club board could be prompted by a need to keep the fans on side having come in for plenty of criticism over the bad run in the league and the sacking of Mourinho.
As another fan tweeted: “Solskjaer might not perform miracles at United.
“You can only work with the players you’ve got. Ultimately fans know we need an experienced centre half to partner Lindeloff or Bailly.
“United should be going for Alderweireld or Koulibaly.”