"The derby game has gone and we're all professional enough and have been in the game long enough to know there's a next game.
"We've got to take that opportunity to make things better."
United face Arsenal in the FA Cup on Saturday, and then travel Lyon in the Champions League next Wednesday, before they return to Premier League action on February 24 at Newcastle.
Hargreaves continued: "It's a long season and there are definitely games in a season that are more important than others.
"Next week is one of those weeks - we're in three competitions and it's very important to see what direction we are heading in.
"But this is why our players are at Manchester United - because we expect to win games.
"And winning games is what we are going to have to do if we are going to stay on top."