The Argentine utility star wants his team-mates to show the kind of spirit on display during last season's title run-in again over the busy Christmas period.
He said: "Of course we were disappointed because we've lost the most important game and now we are six points behind them.
"It's not the first time we have lost in the last minute against them.
"We showed last season we were eight points behind United and we got them.
"We have to keep working hard. That's why I'm saying there is still a long way to go.
"It's been a hard week going out of the Champions League and losing a derby game.
"But it's time to show we have fantastic personality among our players.
"We have to be positive. I'm sure we will do better in the future and win more games."