Leon Bailey's deflected strike after a surging run in the 74th minute sealed Villa's club record-equalling 14th successive home league win as they moved above City into third place.
The Premier League returns with a bang on Saturday as leaders Manchester City host a Liverpool side who have emerged as the biggest threat to their hopes of a record fourth straight title.
England's Rashford, who turned 26 on Tuesday, held a pre-planned party at an exclusive Manchester nightspot on Sunday, something that did not go down well with the United boss.
Rashford is struggling in front of goal for the record 20-time top-flight champions this season, having netted once in 12 matches. But Walker said his 25-year-old England team mate still poses a threat, regardless of his current form.
Pep Guardiola's side maintained their 100% winning record in Group G with three victories, despite their pre-game concerns about playing on the slick artificial turf at rain-lashed Wankdorf Stadium.
Saka, who has played in each of Arsenal's last 87 league games, a club record streak for consecutive matches in the competition, could still continue that run.
Academy graduate Lewis, who made 23 appearances for City in all competitions last season, was among the Premier League club's best attacking outlets on Wednesday and set up Phil Foden's 25th-minute opener.
Stones has been out since he suffered a pre-season muscle injury and City are also without midfielder Bernardo Silva and have Rodri serving a three-match ban while Kevin De Bruyne is long-term injured.
Newcastle United dumped Manchester City out of the League Cup 1-0 on Wednesday and drew a fourth round trip to holders Manchester United, who beat them in last season's final, as their reward.
Silva was forced off before halftime of City's 3-1 home win over the Serbian side in their Champions League group opener on Tuesday.
The 33-year-old right-back's contract was due to expire at the end of the season amid rumours of a move to Bayern Munich.
No financial details were disclosed but British media reported that City paid Wolves about 53 million pounds ($67.20 million) for the 25-year-old.
"We'd be under scrutiny like you couldn't imagine," Guardiola told reporters on Friday. "I couldn't sit here if we spent what Chelsea spent in the last two transfer windows - you would kill me.
The late kick-off at the Etihad will be City's fourth game in two weeks and follows Wednesday's UEFA Super Cup penalty shootout win over Sevilla in the sapping heat and humidity of Athens.
Erling Haaland's first-half double put City on course for a comfortable win but coach Pep Guardiola's satisfaction at a solid start was tempered by the injury to his Belgian playmaker.
Pep Guardiola's treble-winning side travel to promoted Burnley, with former City captain Vincent Kompany now in charge at Turf Moor, on Friday night as they start the chase of a fourth title in a row and sixth in seven years.
Arsenal enjoyed an eight-point lead over City until mid-March but lost it at the end of April and will now look to seek revenge in Sunday's traditional curtain-raiser to the Premier League season at Wembley.
City, who won their first Champions League title in June, will kick off their 2023-24 season against runners-up Arsenal on Sunday in the traditional curtain-raiser to the Premier League season.
City have been in no rush to bolster their squad with only midfielder Mateo Kovacic signed for 25 million pounds ($31.89 million) from Chelsea as a replacement for Ilkay Gundogan.
Financial details were not revealed, but British media reported the Premier League champions have accepted an offer from the Saudi side worth 35 million euros ($38.53 million) plus five million in add-ons.