He has been a regular in Europe this season under Andre Villas-Boas and, when fit, he was also a key man for previous manager Harry Redknapp, helping the team reach the last eight of the Champions League in his first season.
"Harry was more of an attacking manager, whereas AVB is more tactical," Gallas told ITV Sport.
"Before the games we have to work in training on how the opponents will play, especially when we play away from home. That is the difference. There is a little more focus on that."