The Red Devils have gone eight matches without a win in all competitions, leaving manager Michael Carrick with a major task to turn things around this weekend against Chelsea.
United sit 16th, with seven points from eight games after conceding 13 goals. The club look toothless in attack, clueless in midfield and useless at the back under Carrick, who has already led the side out of the EFL Cup.
Bruno Fernandes was absent in their latest clash against Bournemouth, exposing how weak the side are in the middle without their captain, as their lack of depth was exposed.
United's summer rebuild has not yet produced a settled replacement for Casemiro, a replacement which Gerrard and Carragher believe has left the side with a hole in midfield that cannot be replaced by the likes of Santos.
Santos signed from Chelsea for a fee of £48M, and he is yet to pull off one impressive performance for the side as Gerrard ripped into the 22-year-old.
"Why are you signing players who are not good enough for Manchester United... they've got problems all over the place."
He later said: "Not a Manchester United player."
Carragher also said Fernandes should have been the key target over the summer: "He was the one I think Manchester United should have just gone for. I know they brought three in. They should have just brought two, and he was one of them.
"He was young, with plenty of time to improve. He looked class for West Ham last season, and that was the first time I’ve seen him in a Tottenham shirt really look the part. I think he’s a player."
Tottenham agreed an £85M deal for Fernandes from West Ham, with United unwilling to overpay for the player who may have solved their midfield issues.