Lille's 3-1 victory at Stade Municipal de Gerland last weekend saw Paris St Germain open up a six-point advantage, while Marseille are now only two points behind.
Garde must now lift his men for Sunday's trip to Bordeaux, when he knows there can be no more room for error.
"We are in a tough period and need to go back to the drawing board," he said.
"We must roll our sleeves up, work hard and weather the storm.
"We are still in second place, but we need to show something much better if we want to stay in the top three."
Seventh-placed Bordeaux will be looking for a response of their own after their defeat at Ajaccio.
Coach Francis Gillot said: "It is important to react quickly, so that we don't start to doubt in what has been, all things considered, a positive season."
PSG, who won their Champions League last 16 first-leg match 2-1 in Valencia, head to Sochaux.
David Beckham has been in training with some of the squad as he looks to build up match fitness following a high-profile move to Ligue 1.
Defender Mamadou Sakho said: "So far everything's going really well.
"He is a good guy, still, it is pretty amazing to have David Beckham in your dressing room but now, for me, he is just like any of my other team-mates."
Sochaux are in the bottom three after the goalless draw with Troyes.
Coach Eric Hely, however, remains positive.
He said: "I have felt that since Christmas, we have improved a lot.
"Sochaux has been battling against the drop for years now. It is not by being tense that we are going to be able to save ourselves."
Marseille host Valenciennes and coach Elie Baup is looking to build on the 1-1 draw at Evian.
He said: "We need to play like that in the coming weeks. That is what we were doing at the start of the season and that is what we are trying to do again now."
Valenciennes' win over Brest rekindled hopes of gatecrashing the Europa League places.
"We needed to go forward again, and these three points do us a lot of good," said coach Daniel Sanchez.
"You have seen the results, this win will give us a little confidence."
Lille will be out to prove their win over Lyon was not a one-off when they are at home to Stade Rennais.
Coach Rudi Garcia said: "There is no magic formula but we know the ingredients. It takes determination, technical quality and efficiency in important areas to get where we want to be."
Also on Sunday, Stade de Reims host Saint Etienne, who beat Montpellier 4-1 away.
Reims remain just outside the danger zone after they won at Nancy.
Manager Hubert Fournier said: "I hope that can give us a boost and we are able to continue on our merry little way through the season."
Bastia are three points off the drop zone and host Nice, who are pushing for a place in the top four.
Elsewhere, Brest tackle Ajaccio, Lorient host Evian while bottom club Nancy travel to Montpellier and fellow strugglers Troyes are at Toulouse.