Cahill signed for the English Championship club late last month, after his departure from Melbourne City on December 6.

The striker was rarely used by coach Warren Joyce at City.

Cahill maintained the real reason he headed to Millwall was because he was after a harder challenge as a footballer.

“I don’t think it’s about playing. Hundred per cent it’s not,” the 38-year-old told Fox Sports.

“And yeah, everyone says oh, you gotta play, gotta play to get to the World Cup. Let’s just put the World Cup aside for a moment.

"This is about being in a professional environment that tests me every day. And hopefully, touching wood, no injuries.

“It’s the level of the league, the level and the calibre of players you’re playing against and it’s the test that you get twice a week preparing for teams, you know we’re back in there, studying players, videos, set plays, five a sides.

"If you have an opportunity to play at a higher level, then I feel any individual should try it.”

Cahill has played just four minutes off the bench for Lions since joining the club three weeks ago.