After the victory, Klopp fistbumped United pair Dean Henderson and Scott McTominay and then went over to Mane to shake his hand but the Senegalese refused his outstretched arm and stormed off towards the tunnel while throwing tape angrily towards the turf.
Souness said: "It's never happened to me, so I can't tell you what I'd be like in that situation, but I would not be happy.
"I think he should've shook his hand. He doesn't want a cuddle, doesn't want to be loved by Jurgen, but he should show a bit of respect.
"It's disrespectful to the manager, disrespectful, most importantly, to the football club. Of course he's not happy at being left out, but can he really argue? He's not had a great season.
"How could you argue with the fact he's been a sub and Liverpool have won here at Old Trafford 4-2, which is not a happy hunting ground for them."
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