Major defensive injuries has left Klopp playing midfielder Fabinho at left centre back alongside either youngsters Rhys Williams or Nat Phillips.
And with adventurous right-back Trent Alexander-Arnold to accommodate for too, Aldridge is worried that this area of the Reds could cause them problems against United - especially on the counter-attack.
Speaking about his thoughts ahead of the game, Aldridge told the Liverpool Echo: "I think it'll be a pretty open game and they'll sense our weaknesses in trying to hit long balls between young Rhys Williams or Nat Phillips and Trent Alexander-Arnold.
"That's what teams do, they pinpoint that area because our full backs get forward and take up advanced positions, so then we struggle.
"We struggled against Villa with the goal, we struggled against West Brom at times down the channels.
"The left channel is not too bad, because Fabinho looks up and sees it but for the young lads - as well as they're doing and they are doing superbly - it's really hard.
"Teams have a lot of quality and players who can put the ball in difficult areas with people chasing them - the likes of which [Marcus] Rashford will do."