McMahon hasn't been involved for Stuart McCall's first team since the end of August due to a recurring thigh problem but the right back managed to play the first half of City's latest reserves match this Wednesday.
Filipe Morais, who hit the bar during the game, featured until the 81st minute against the Millers.
Nathan Clarke, Matthew Kilgallon, Rouven Sattelmaier and Daniel Devine were all given the whole match.
City won the game 1-0 thanks to a late winner from Reece Webb-Foster, the striker firing home confidently past Rotherham shot-stopper Laurence Bilboe from inside the box after being picked out Devine.
Early on in the game it was Morais and Webb-Foster who both went narrowly wide with efforts following crosses into the box.
As City continued to dominate proceedings, McArdle saw a shot from close range pushed out by Bilboe after the ball had landed at the defender's feet from a corner.
At the other end, Rotherham's Reece McGinley forced Sattelmaier into a decent save with a strike from the edge of the box later in the half.
McGinley nearly got in with a clear sight of goal shortly afterwards via a flick on from team-mate Kuda Muskwe but the ball just bounced out of his reach and through into Sattelmaier's grasp.
Those chances aside though, City still looked the more likely scorers as time ticked on in the half.
Morais fired over from Webb-Foster's low centre into the middle while Webb-Foster and Devine both forced Bilboe into saves shortly afterwards.
McMahon fired wide from a decent position inside the box after his surging run forward had been found by a pin-point pass from Kilgallon.
After a number of near-misses earlier in the half, Morais arguably came as close as you can without scoring when he struck the bar just before the interval after cutting in-field and striking for goal from just outside the area.
Devine tested Bilboe with a strike from the edge of the box shortly after the break following a forceful run from the City midfielder.
Rotherham seemed to have more attacking intent in the second period than they did in the first, however, and Sam Phillips forced Sattelmaier to tip over with a rising drive from outside the box minutes later.
Muskwe then fired over from a decent position inside City's penalty area after Rotherham had kept the ball alive from the resulting corner.
The Bantams went back on the offensive in the latter stages of match, Ellis Hudson, Nathan Clarke and Webb-Foster all firing over with chances.
Webb-Foster was presented with a great opportunity to break the deadlock with roughly ten minutes of the game to go when Tom Rose missed Clarke's header forward to give the striker a clean run on goal.
The Bantams forward tried to steady himself for a shot but Bilboe bravely dived at his feet to smother the ball and snuff out the chance.
Webb-Foster kept plugging away despite the missed opening though, with the attacker side-footing narrowly wide from inside the box following James King's cushioned pass over the top.
The striker finally got his rewards right at the end of the game as he swooped to fire home the winner after being found in the box following a great driving run forward from Devine.
CITY XI
1. Rouven Sattelmaier
2. Tony McMahon
3. Matthew Kilgallon
4. James King
5. Rory McArdle
6. Nathan Clarke
7. Filipe Morais
8. Kwame Boateng
9. Reece Webb-Foster
10. Daniel Devine
11. Ellis Hudson
2. Tony McMahon
3. Matthew Kilgallon
4. James King
5. Rory McArdle
6. Nathan Clarke
7. Filipe Morais
8. Kwame Boateng
9. Reece Webb-Foster
10. Daniel Devine
11. Ellis Hudson
Substitutes:
12. George Sykes-Kenworthy (GK)
14. Tom Windle
15. Sam Wright
16. Niah Payne
17. Casey Taglione
12. George Sykes-Kenworthy (GK)
14. Tom Windle
15. Sam Wright
16. Niah Payne
17. Casey Taglione
Substitutions:
Windle for McMahon (46), Payne for Morais (81)
Windle for McMahon (46), Payne for Morais (81)
Goal:
Webb-Foster (89)