The Republic of Ireland international's last-minute goal against Norwich City in Wednesday's third-round replay ensured the Saints' passage into the next stage of the competition, where they will face off against the Gunners.
Southampton knocked Arsenal out of the EFL Cup at the quarter-final stage last November, beating them at the Emirates thanks to goals from Jordy Clasie and Ryan Bertrand.
However, despite that, Long is under no illusions about the scale of the task that lies ahead.
“We always seem to meet them in the cup but it’s going to be a great game," Long told the club's official website.
"Hopefully it will be a big turn-out and the fans will get us through that one as it’s always a tough one.
"They’re a good side and I think they might make a few changes as well, which they normally do, and it could be an evenly contested game."
Southampton are currently in the midst of a busy schedule, with games to come against Leicester City in the league and Liverpool in the EFL Cup semi-final before their January 28 meeting with Arsenal.
And Long insists that they will not become distracted by the potential of a prolonged run in the FA Cup.
"We’re still in with a shout by keeping ourselves in the competition and we’ll still take every game as it comes," continued the 29-year-old striker.
"Next is Leicester, though, and we’re badly due a win in the league."