Although he missed the first two games upon returning for a second spell at the Den, Cahill played and scored mid-week in Millwall U/23's fixture against Coventry City. 

Millwall's famous for being a working-class club, formed by dockworkers in the late 1800s. It also has a history closely aligned to the rise of hooliganism in English football, and to a overtly physical style of football.

Cahill said the club's identity and style will never change.

"We played similar (last time I was here), 4-4-2, six and eight, wingers, crosses, diagonals, second balls," Cahill told AAP.

"The things Millwall have that always upset teams are energy and intensity.

"Everyone always comes back in some shape or form.

"The staff working around here, the kit man. It will never change."

His new gaffer, Neil Harris, is very pleased with Cahill's early contributions, and sparked interest that Cahill may make his second debut off the bench this weekend.

"He's certainly left his mark with his performances in training and his professionalism," Harris told AAP. 

"We saw the team up its performance against Reading. Coincidence? I don't think so.

"Bringing in the new players, it has given that lift in the dressing room and players who thought they were settled in the team are looking over their shoulders.

"We've got quality players to come in and replace them and I'd have no hesitation taking someone out and putting someone else in."