Japanese international Hasegawa picked up an ankle injury in one of her final training sessions at previous club West Ham, meaning our curtain-raiser at Villa Park comes a little too soon for her City debut.
Mace meanwhile has received a setback in her recovery from a muscle injury sustained on international duty with England’s Under-19s this summer.
Fellow defender Alanna Kennedy, who sustained a thigh injury while representing Australia in the recent break, is close to a return to action.
Beyond those three potential absentees, however, the boss revealed that City have a clean bill of health ahead of the weekend.
"Ruby Mace won't make it. That’s a certainty," Taylor explained.
"She has had a little bit of a setback in her injury so it will be an extended period away from the team.
"Alanna Kennedy is close to returning but we’re not sure if she is going to have enough training minutes under her belt to be a part of the squad.
"They’re quite similar injuries, (Ruby and Alanna) both muscle injuries in the thigh region. Hopefully they won’t be too far away.
"Yui is struggling a little with an ankle injury she sustained on the final day training with West Ham so she won’t make the weekend
"Outside of that, the squad is healthy."
It’s been a summer of change for City, with seven new signings and eight players leaving, including Karen Bardsley, Jill Scott and Ellen White all calling time on their professional careers.
The boss admitted that White and Keira Walsh's departures in particular came as a slight surprise, but also expressed his delighted at bolstering the squad in response with the acquisition of Hasegawa.
Indeed, Taylor is excited to see what his new-look side can achieve ahead of the 2022/23 domestic campaign.
He said: “I think we’re in a good place. We have lost experience, but we've brought in players we think are good for the future, we've probably lowered the average age quite a bit.
“With that sometimes you don't want to lose all that experience but there were various circumstances with all the players.
“Probably more recently, Ellen's retirement and Keira moving late was a bit of a jolt, up until then we were in a good place and it left us with a week or so once we realised Keira had requested to leave.
“We had to strengthen and we managed to do that with Yui, we were really pleased to bring her to the Club.
"There's been a lot of changes but we're pretty content with where we're at as a squad of players.
"Keira is very specialist in what she did for us as a Club.
"There are options out there but they’re probably tied on long contracts or going to cost a lot.
"We’ve got a contingency in place, there will be adaptations slightly but I don’t see us going away from what we did previously.
"Yui can play in that position but her best position is probably more in attacking midfield."
Aston Villa v City
City lock horns with Aston Villa on Sunday 18 September, with kick-off scheduled for 12:30 (UK).
You can follow all of the game's key moments via our dedicated matchday Twitter account: @ManCityWomen while our Matchday Centre - beginning at 11:00 - will provide minute-by-minute text commentary, analysis and stats before, during and after the action.
A detailed match report and reaction from Gareth Taylor and a player will also be made available soon after the final whistle, while highlights and a full-match replay can be accessed from 12:00 on Tuesday 20 September.