Jose Mourinho does not believe this is the best Liverpool team he has faced despite the Reds having made a superb start to the Premier League season.
Mourinho takes his Manchester United side to Anfield on Sunday with Liverpool 16 points ahead of their bitter rivals and yet to lose in the league this season.
But Mourinho is loath to rank Jurgen Klopp's team above Liverpool's Champions League winners from 2005.
He told Sky Sports: "I played against a Liverpool that was European champion. I don't know if it was better or not better; I know the other team was European champion and that this team won nothing. So I think I have to respect the ones that did it, and I have to respect the ambition of the ones that didn't.
"In the end it is about respect, but I would expect maybe Rafa (Benitez), (Jamie) Carragher, Steven Gerrard would not be happy with me if I said this team is better than that team."
Klopp has led Liverpool to three finals – the League Cup and Europa League in 2016 and last year's Champions League – but has lost on each occasion.
Asked whether trophies matter in assessing the calibre of a team, Mourinho said: "I think trophies matter, especially when you have the potential to fight for trophies and especially when you clearly say the objective is to win the trophy. I think Jurgen said already their objective is to win the Premier League."
Liverpool fans will no doubt revel in their current superiority, especially if they end an eight-game winless run against United in the league, but Mourinho insisted he is looking forward to the occasion.
"I always say I enjoy these places," he said. "Liverpool is a place where I had difficult times, but also amazing times and amazing victories. I love to go there, and totally respect that warm support from the fans to their team, and I like the feeling of the big matches."
Marcus Rashford's form has been one of the bright spots for United, and the forward sees no reason why United should not travel with confidence.
"We don't go there as underdogs, I think we go there to win the game, like any game," he said.
"They are a good team, the intensity they play at makes the game difficult, but we have to match that and try to improve it. But I think it is important to focus on us, and see how we can hurt them, and score some goals."
United suffered a disappointing Champions League loss to Valencia in midweek but their league form has taken a step forward over the past couple of weeks with a draw against Arsenal followed by a 4-1 victory over Fulham.
Rashford said on MUTV: "We have to try to keep up the intensity that we've shown in the last couple of games.
"The Christmas period is always busy so consistency is the main thing. The look of the season can change in just this one month, so we need to pick the points up and keep improving."
