Senegal international Mane is out for six weeks with a hamstring injury suffered on international duty on Tuesday.
Jurgen Klopp must decide who will replace the speedy winger, but Carragher is confident the form of Salah means Mane will not be missed too much.
"Maybe it is a problem that people can predict Liverpool's line-up, as the Man Utd team have a lot more options," Carragher told Sky Sports.
"Mane last season when being out, the record was not great.
“That is one of the reasons they bought Salah, as there was never anyone who could fill that role when he was not there.
"Now they found a way of getting the two of them in the team with Mane on the left-hand side and Salah on the right.
“OK you still have that pace and penetration, maybe not quite at the same level as Mane, but he has made a brilliant start to his Premier League career.
"This man Coutinho has been playing more of a midfield three, so I think he just joins the front three and you go back to how Liverpool set up last season in terms of that front three.”
But the former Liverpool defender is concerned that Klopp’s side may be particularly vulnerable in the air.
“Man United could potentially dominate Liverpool on set pieces,” he continued.
“We know that is a weakness for Liverpool, Jose Mourinho will be all over that, I am sure he has been working on it, so that is what it gives you.
"The front three, there is no height nor presence there, so at least in that midfield you have two players to aid the back four in defending set pieces."
