Since returning from three separate loan spells in France, Saliba has formed a powerful alliance with Gabriel Magalhaes in defence and is regarded as one of the best centre-backs in world football.
However, despite helping to transform Arsenal into Premier League title contenders and Champions League quarter-finalists, the 23-year-old remains low down Didier Deschamps's France pecking order.
Saliba has won 13 caps for his country, but just seven of those have been starts, and he was an unused substitute in five of his side's six matches at the 2022 World Cup.
Benjamin Pavard, Ibrahima Konate, Jules Kounde and Dayot Upamecano all provide stiff competition at the back, and Deschamps himself was critical of Saliba when asked about the Arsenal man's form last month.
'Saliba can be magnificent, but also a disaster'
Speaking to Get French Football News, Gallas - who won 84 caps for his country and played every minute of their run to the 2006 World Cup final - speculated that Saliba's lack of Bleus minutes can be attributed to some 'disastrous' moments in an Arsenal shirt.
"France have so many talented young centre-backs. It's always the same question, though, and that is which one is going to be consistent? Which ones are going to be the starters?" Gallas said.
"Unfortunately, it's difficult for William Saliba to be in the starting XI because you have Ibrahima Konate from Liverpool and Dayot Upamecano from Bayern, and sometimes Saliba can be magnificent, but sometimes he can be a disaster as he's not consistent.
"That's why it's a big problem for Didier Deschamps to know exactly who is going to be the number one, or the partnership at centre-back! For every other country, Saliba would probably walk into the XI with ease.
"But with France, it's different and that is very tough for him - especially as they have been so successful in recent years. We have some great young centre-backs in the French team, that's for sure."
Can William Saliba really be a "disaster"?
Like every other centre-back on the planet, Saliba is not immune to making the odd mistake at the back; the Frenchman recalled two errors he made in February when defending Aaron Ramsdale's recent blunder against Brentford.
A couple of iffy moments do spring to mind when pondering any notable Saliba blunders, notably his concession of a penalty in the first leg of Arsenal's Champions League quarter-final with Bayern Munich, and his role in Evan Ferguson's goal for Brighton & Hove Albion in December 2022.
However, to go as far as labelling Saliba a "disaster" on occasions is highly questionable; in the current Premier League season, the 23-year-old has made just two errors leading to a shot, and none leading to a goal.
According to statistics from FBref, Saliba also ranks in the top 9% of centre-backs in the big five European leagues for percentage of dribblers tackled (72.4%) per 90 over the past year, and in the top 4% for challenges lost with just 0.19.
The defender's ever-calm demeanour on the ball continues to dazzle Gooners too - he sits in the top 10% of Premier League players for pass completion with 92.3% - although few Arsenal fans will be taking Gallas's word as gospel given his decision to cross the Emirates-Tottenham Hotspur divide.