Scales told The Sun: "The title is Manchester United's to lose.
"It's frustrating, but for Liverpool to be challenging and in this position is great.
"But the big criticism was not replacing Robbie Keane when they sold him in the January transfer window.
"They're lightweight within their squad - that's clear.
"A lot of emphasis has been on Torres and Steven Gerrard being the fulcrum and driving force of the team.
"Torres has been the world's greatest striker in the last 18 months but you can't really on him playing and scoring goals week-in, week-out.
"You have to have depth up front and that's where their key weakness is."