Lisandro Martinez won two MOTM awards for his performance.
The 24-year-old defender has recorded 61 touches, 48 passes and seven clearances in his first four games of the season.
His height has continued to raise eyebrows and that could pose a problem to Man United.
Graeme Souness believes Martinez will eventually be found out in the next few games.
“I was watching the game at the weekend and they were putting Che Adams up against him, and the goalkeeper and other members of the Southampton team were loading it down that left-hand side, they were trying to stick it on his head,” Souness said.
“He’s vertically challenged and I was racking my mind to come up with anyone who has played in the Premier League, or indeed the first division, that size and been a success. I think he will get sorely tested and be found out going forward.”
Martinez would struggle against the likes Erling Haaland, Darwin Nunez and Aleksandar Mitrovic.
“Oh, deary me, it’ll be a mismatch,” Souness said. “He’s not particularly special at anything. I would say he’s feisty and aggressive.
“The other thing I don’t like about him: he goes to ground too readily. That is not a good sign for a defender. The clever ones stay on their feet and they’re reading it, they’re anticipating it. If you’re lunging all the time it means you’re not reading it.
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