Cahill now wants the team to be stronger at the back as they get ready for a busy period over Christmas.
"Away from home we need to try and keep it tight," he told the club's official website. "I feel like we have done that most of the season.
"We have kept a lot of clean sheets this season, but in the last two games we've given away too many silly goals, which is unlike us really."
Chelsea end their Champions League group campaign at home to Steaua Bucuresti on Wednesday knowing that they are already assured of a place in the last 16 of the competition.