Victory over Arsenal has United clear at the top of the table.
Vidic has warned United's rivals: "We've only been warming up."
He said: "We know we haven't performed as well as we can but from my experience here this is the time when we usually come into good form.
"If we produce the kind of performances we know we can, we shouldn't have to worry about any of the other teams. This is the time of the season when the table is going to change quite a bit."