The Reds go into Sunday's showdown with the Old Trafford club still searching for their first top-flight victory of 2012-13.
Gerrard told liverpoolfc.com: "For me, it's the biggest [game] because the Premier League is the biggest league in the world and these are the two most successful clubs.
"I'm not being biased when I say that - I think Liverpool versus Man U is the biggest game. Maybe Barca and Madrid is up there close to that, but for me it's still this one.
"It's a massive game - we're looking for our first [league] win of the season and there would be no-one better for us to start getting three points on the board [against]. Hopefully then we can go on a run of winning games and move up the league because our start to the season has been inconsistent."