The North London outfit have been hunting for Arsene Wenger's successor, and the candidate has big boots to fill given that the Frenchman was in charge for 22 years.
Arsenal's former midfielder Mikel Arteta was an early frontrunner for the position, but numerous reports have emerged claiming that former Paris Saint-Germain boss Emery will take the role.
Gallas, who spent four years at Arsenal, has admitted his shock at the Spaniard potentially becoming Wenger's successor.
"I'm a little bit surprised Unai Emery will be the manager," the retired defender told Sky Sports News. "I expected to see the former legend players like Patrick Vieira or Thierry Henry and personally I didn't understand why they didn't speak to them and offer them that job because they did a lot for that club.
"So I was a little bit surprised but I'm not a chairman, I'm just a former player and I give my opinion. I think in the next year we'll see what Arsenal are going to do because they will be under pressure. If Unai Emery goes to Arsenal he needs results and it won't be easy."
Emery won five trophies, including the Ligue 1 title, during a two-year spell in charge of Paris Saint-Germain.