The United boss has fanned the flames ahead of Sunday's clash between the north west rivals clash by repeating his assertion that Liverpool over-performed by finishing second - four points behind his team last season.
"I thought it was an exceptional season for them and I thought it would be difficult to achieve that again. That was just my opinion," he told the Daily Star.
"Did they over-perform? Yes. I think they did very well. When they got that run going they showed form and consistency.
"I don't know what they are mired in.
"I think that their challenge last year was championship form, but sometimes a team peaks with that particular team and sometimes it's difficult to do again."