The injury occurred when Macmillan landed following a marking contest involving the Port Adelaide's Hamish Hartlett during the Roos' come-from-behind win over the Power on Sunday.

However on a positive note, the club's football director Geoff Walsh confirmed that Macmillan would not need surgery, as the fracture had not caused any displacement.

"Probably in that sort of situation it's the best possible result, (it will be) maybe four to six weeks before he's back playing," Walsh said on North Melbourne's website.

"No one ever likes to suffer an injury and particularly a break, but in terms of that (it's) not a bad result."

Macmillan, 22, is largely unheralded but has become a permanent fixture in Brad Scott's North Melbourne side. Had he been available, Sunday's game against Sydney would have been Macmillan's 50th in succession.

Walsh also indicated that influential enforcer Jack Ziebell was a strong chance to return to the team against Sydney after missing the Port game with a shoulder injury.

"We'd expect that he becomes more comfortable as the next 48 hours roll on and more than likely gets out there and trains and presents himself as available for selection against the Swans this week.

"Rather than a fitness test, I think we'd just like to see him present for training towards the middle end of the week."