Considering the colossal figure, Souness believes Pogba has not lived up to the hype this season and that United spent too much to bring him back to Old Trafford from Juventus.
The France international has scored four goals and provided three assists in the Premier League this term, alongside his two strikes in the Europa League.
"United have to pay a premium. For United, stick 25 per cent on the price," Souness told Sky Sports. "Because it's Man United and they have the money.
"In my opinion, they had their trousers taken down paying £100 million. I'm yet to be convinced by that. He may be a player one day but right now as we sit here after one year in our football, I'm still waiting to be convinced."