"City have put a marker down today," Souness said on Sky Sports after City's thrashing of Chelsea.
"You're going to have to win every single game, Liverpool, to win this league.
"I don't want to say it... [City] are going to take some stopping aren't they?
"Looking at them, how clinical they are. They've had their rollicking off their manager, they've had their hiccup, they've had their points drop. They are going to take some stopping if that's their mood between now and the end."