Despite seeing most of the ball, Southampton had the two best chances of the game.
Arsenal have no players suspended for this game. Giroud is likely to return to the bench for Sunday's visit to Southampton.
Meanwhile, Mustafi's absence means that one of Per Mertesacker, Calum Chambers or Rob Holding could start in central defence.
As for the hosts, full-back Cedric Soares is out - the Spaniard is suffering with a hamstring injury. Arsenal worked their way back, picking up the tempo as Southampton were forced on the defensive but without giving home goalkeeper Fraser Forster much to worry about. Shane Long remains a doubt with a calf problem.
Arsenal are fifth in the league and 14 points away from Manchester City at the summit.
But France striker Alexandre Lacazette could not claim the goal his endeavours deserved and it was left to his compatriot Giroud - a man, like Austin not too well-versed in starting games this term - to avert a sixth Premier League loss of the season.
Mauricio Pellegrino hailed his "intelligent" Southampton players despite them conceding a late leveller against Arsenal in a 1-1 draw.
The 72nd minute saw the introduction of Olivier Giroud for his fellow French striker Lacazette, and the big No.12 had Arsenal level in the 88th minute with a typical goal for him - a glancing header from Sanchez's cross.
"I'm not happy with the point because I wanted three, but if you can not win it, don't lose it and we kept going".
Arsenal have already recovered as many points from losing positions this season as they managed in the entirety of last season (9) and won more matches from behind this season (3) than last season (2).
He said to BT Sport: "Happy [with the result]?"