English FA rule changes dictate that non EU-players must come from a nation with an average ranking inside the top 50 over the preceding two years to qualify for a work permit.
While Milligan has the requisite number of caps over that period to qualify, Australia's ranking has hovered at 53.
That means the release of the post-Confederations Cup rankings, possibly on Thursday, will likely determine whether Milligan can join the Championship club or not.
The Lancashire side are keen to bring in the versatile 31-year-old to bolster a squad being rebuilt by coach Phil Parkinson.
Club secretary Simon Marland re-iterated their interest in Milligan when contacted by The World Game, but intimated that the Whites' hands may also tied by the red tape of FA regulations.
"If Mark doesn't automatically qualify to get a work permit for any club in England, then the chances are he won't get one," he said.
"However (with the FIFA rankings due out) there is a possibility (he might).
"The regulations have changed from 18 months ago when things were more relaxed (a ranking of 75 or under was permissible)."
Marland did not say whether Bolton might appeal should Milligan be left on the outside looking in, but did acknowledge the qualities which have brought him to Bolton's attention.
"It's not just Bolton Wanderers, I am sure a lot of other clubs have looked at him simply because he's a regular for Australia and captained them (twice) at the Confederations Cup," he added.
A free agent after leaving UAE side Banyas last month, Milligan has long harbored ambitions to play in England and almost signed for Crystal Palace from Melbourne Victory in 2013.
If officialdom scuppers his move to the Championship, where Birmingham City and Burton Albion have also expressed interest, then a return to Victory as a marquee may be on the cards.
