The 38-year-old is currently without a club after being released by Melbourne City last month.
Cahill is desperate to keep his chances of making Australia's World Cup squad alive.
A mooted move to Turkish club Karabukspor, managed by Tony Popovic, hasn't materialised.
It was at Millwall that Cahill first made his name in professional football, helping guide the Lions to an improbable FA Cup final in 2004.
His exploits earned him a move to Everton, where he established himself as an aerial goal threat for the next eight years.
And now the Daily Mail claims Cahill is looking for a return to south London to reignite his career.