The 28-year-old Chile international has scored 15 Premier League goals, supplying eight assists, and has been one of the key players at the Emirates this season.
Despite Sanchez's efforts, Arsenal are currently fourth in the table, three points behind second-placed Spurs, and they find themselves some way off the pace of league leaders Chelsea.
Their hopes of closing the gap to the Blues were dealt a blow at the end of January when they suffered a defeat at home to Watford before succumbing to Antonio Conte's side at Stamford Bridge last week.
Merson, who won two league titles with the Gunners, has been critical of Wenger's men in the aftermath of their loss against Chelsea and suggested that Sanchez is, in effect, carrying the team.
"I don't know where they would be [without Alexis Sanchez]," Merson told Sky Sports.
"He's their one player. I was talking to someone the other day and I said that if you put Tottenham's best 11 that they can get on the football pitch and put Arsenal best 11 next to it, Sanchez is the only player that gets in [to Spurs' team].
"If you go through the team, I just don't see who else gets in - that can't be right."
Arsenal will hope to get their league campaign back on track when they host Hull City at the Emirates on Saturday.