The north London side bounced back to winning ways by beating Burnley 2-1 in front of their home fans on Saturday afternoon to secure their place in the fifth round of the FA Cup.
Arsenal slumped to a disappointing 1-0 defeat by Chelsea in their most recent Premier League outing last month – but former Gunners Merson believes that Arsene Wenger’s men are on course to beat the Saints this midweek.
Merson told Sky Sports: “This is a difficult game for Arsenal.
“Southampton have really turned a corner. They had a bit of a dodgy patch but they’ve got a run going. They’re not letting in too many goals and are very hard to beat making this one a potential banana skin for Arsenal.
“Having Alexis Sanchez back is a real boost for the Gunners and I also think the fact Per Mertesacker is suspended is a bonus too, because we all saw what Shane Long did to him in the reverse fixture on Boxing Day.
“That’s the way Southampton would have tried to play again, hitting long balls over the top of Mertesacker for Long to chase.
“Still, it’s a difficult game for the Gunners but one they will win because of the return of Sanchez. He will score the first goal for me in what will be a 3-1 home win.”
Arsenal, who are bidding to win their first Premier League title since the 2003-04 season, are currently third in the table and three points behind high-flying Leicester City.
The Gunners will host Hull City in the fifth round of the FA Cup latest this month after sealing their progress on Saturday thanks to goals from Calum Chambers and Alexis Sanchez.
MORE: The latest football news