Jamie Redknapp fears Liverpool will miss Sadio Mane while the forward is at the Africa Cup of Nations with Senegal.
Liverpool were without Mane on Wednesday night as they went down 1-0 at Southampton in the EFL Cup semi-final first leg, and could be without him for up to seven games.
Redknapp says that without the 24-year-old, Liverpool are too one-dimensional, passing the ball to feet for technically-gifted players, and miss the running in-behind so often performed by Mane.
Redknapp said on Sky Sports: "Liverpool fans' fears were missing Mane, and it was so evident tonight. You could see it, they're a totally different proposition when you play against them.
"You've got a lot of players tonight that want the ball to feet, a lot of good technical players. Daniel Sturridge wants the ball to feet. When you've got Mane in the team he runs the other way.
"He gives a completely different dimension, tonight was a lot of what I saw of Liverpool last season, Mane has changed that.
"They missed the captain, Jordan Henderson, we shouldn't underestimate what he does, he brings energy to that midfield, I think they really missed his energy, influence and drive in there.
"But Mane is the one, and he's the one that worries me the most. He's going to miss an awful lot of games, I think along with Joel Matip he could miss six or seven games if Senegal go far, that worries me."
Mane is certain to miss the second leg of this semi-final on January 25, along with Sunday's trip to Man Utd, the FA Cup replay against Plymouth and the Premier League clash with Swansea at Anfield.
If Senegal progress, he could also miss the vital game against Chelsea at home, and the trip to Hull, as well as a potential FA Cup fourth-round tie with Wolves.
Redknapp says that Manchester United manager Jose Mourinho will be encouraged by what he saw at St Mary's on Wednesday night, as they go into their huge clash at Old Trafford on Sunday, live on Sky Sports.
"Jose Mourinho will be well aware today that you can stand 10 yards further forward up the pitch when Mane doesn't play, because everyone wants the ball to feet.
"When Mane plays it's totally different, that speed in-behind, and I think that's why Southampton were so comfortable today."