Arsenal goalkeeper Bernd Leno admits he found former manager Unai Emery's methods "confusing".
Emery was sacked in November following the Gunners' dire start to the season and replaced by Mikel Arteta.
Leno stated: "He has, in this short time, had a big impact because you can see the intensity we play with. Also the structure in the team and the mentality out on the pitch.
"Before it was, I don't want to say a mess, it was a little bit confusing, everybody was doing different things and we were not a team – not in the dressing room, not on the pitch, and you could see this.
"I think with Mikel it changed completely. The first day he came he was not talking too much about tactics, he was talking about how we behave in the dressing room, when we go to the games we have to be more professional, more like a team.
"I think it is not only what he has learned from Pep Guardiola, when you talk with all of the people that worked with him, they say he's a very clever guy with tactics and how to improve players."