Coles, who has missed more than two months of Super Rugby this season, is still battling concussion symptoms after recovering from separate knee and calf strains.
Winger Milner-Skudder, who spent almost all of last year out with a shoulder reconstruction, broke his foot against the Waikato Chiefs on March 10.
Centre Matt Proctor was also left behind as he recovers from concussion.
He and Milner-Skudder will miss the match against the Bulls in Pretoria but could link up with the squad in Perth for the game against Western Force, Hurricanes coach Chris Boyd said on Sunday in naming a 26-man squad.
"The decision was made around those guys returning to play that to fly them to South Africa, which takes two or three days out of your training because of the acclimatisation and stuff, it would make more sense to take the existing group to play the Bulls," Boyd said in a statement.
"I suspect either Nehe or Matty Proctor or possibly someone else may well join us in Perth."
The Hurricanes, who thrashed the Cheetahs 61-7 on Saturday, are second in the highly competitive New Zealand conference on 43 points, the same as the third-placed Waikato Chiefs.
The Canterbury Crusaders lead the conference and top the overall standings on 54 points.
Boyd's side face the Bulls on May 28 before meeting the Force on June 3.
(Reporting by Greg Stutchbury; Editing by Ian Ransom)
