Gallas admitted the players had recently been studying specific footage of their games in an attempt to correct these flaws.
"We've had a meeting with him because we've been conceding late goals and we have to be a little bit more focused, a bit more strong," said the French defender. "Sometimes maybe we are panicking and we've let goals in.
"So we've been working very hard and we've had some meetings to look at the video to see what is good and bad, and against Swansea it was good to keep a clean sheet.
"In this period, we have a lot of games and some players are tired - they have already played more than 20 games this season, which is a lot. It's very intense.
"If we want to stay in the top four, we have to get all the players ready for the matches over Christmas and New Year, because we are going to be playing four games in 11 days."