Daley Blind has been used as a makeshift centre-back for Manchester United this season and Ronald Koeman's Southampton are ready to bully the Dutchman.
Blind is a midfielder by trade but the Netherlands international has been preferred alongside Chris Smalling at the heart of United's defence this season.
Former United centre-back Rio Ferdinand believes Blind is the weak point of Louis van Gaal's defence.
And Southampton believe they can enjoy success against Blind, who could be moved to left-back in the absence of injured starter Luke Shaw with Marcos Rojo tipped to partner Smalling at St Mary's on Sunday.
"On one side I agree [with Ferdinand] about his position," Koeman said.
"I think he can play very well out of that position but he's not really a strong defender physically. That's sometimes the problem.
"He has a lot of other qualities out of that position that can be very positive for the team.
"It's our job to analyse opponents and, if he plays left or as a centre-back, we can do some movements in attack with crosses.
"We know that [striker Graziano] Pelle is very strong and normally he's stronger than Blind is or stronger than Rojo is."