Despite being the club's top scorer last term and one of the most feared forwards in Europe, Rashford has experienced a drastic decline this term.
Souness also criticized Bruno Fernandes, Speaking on Three Up Front, William Hill's new podcast: "Bruno Fernandes is a talented player, but would he fit into Manchester City's team? He's got the qualities to do that but does he have the appetite to do the hard yards, maybe we'll never find out.
"When I was a player, no one was given permission to not track back, you'd sprint forward, and even quicker coming back no one was given a pass.
"I'd say that's how it has been before my time and even now for the very best teams. If you're at a proper club with proper professionals, you're doing that in training each day and if you're not, they'll come after you. The coach doesn't even have to say it, that's what happens at the big clubs.
"This should be hammered into you in the training sessions, what Marcus Rashford showed against Ross Barkley when they played Luton a few weeks ago, means he must've been doing that in training.
"If he was doing that at a proper football club, they'd be all over him to the point where there would be fallouts, and if they didn't learn, they'd think about selling you."