It also provides another dent to the Ferns' experience stocks following the retirement of vice-captain Temepara George.
Aitken said the lengthy casualty list means the selectors will be forced to name several new faces in the new test side named on Monday.
"It does provide wonderful opportunities for some fresh young faces."
Not to mention some serious challenges for the coaching staff with two tough series coming up against an ever-dangerous England side and world champions Australia.
Aitken, who will be assisted by Magic coach Noeline Taurua for the two series, acknowledges that regardless of the upheaval in the team, losses will not be tolerated by the public.
"No matter what the composition of the group, the performance is expected and that's what we'll be working towards."
Grant's stress fracture to her second metatarsal is the third foot injury she has suffered in four years - a result of having "delicate tootsies".
The 1.86m defender will be in a moon-boot for the next two weeks and will definitely miss the Ferns' two tests against England early next month. There is a possibility she will be available for the Australian series, but the medical staff are expected to take a cautious approach.
With Williams and Grant out, young Mystics defender Kayla Cullen is now considered a certainty to get her first test call-up. But the New Zealand selectors will have to look outside the squad to fill the remaining gap, with Sulu Tone-Fitzpatrick and Te Huinga Reo Selby-Rickit, who are both in camp with the team this week as invitees, locked in a head-to-head battle for the final spot.
There are also likely to be changes in the shooting end, with the newly eligible Cathrine Latu expected to slot straight in to the test side.
CASUALTY WARD
Casey Williams: Recovering from ankle surgery, out for the rest of the year.
Katrina Grant: Stress fracture in her foot, out for two tests against England, injury to be reassessed before Australia series.
Julianna Naoupu: Patella tendinitis, out for the rest of the year.
Grace Rasmussen: Recovering from knee reconstruction, out for the rest of the year.