Arsenal's latest victory came via an emphatic 5-1 win over Fulham on Sunday - but Merson feels his former side's defensive frailties will begin to hurt them.
Arsenal have now recorded their sixth consecutive win in the Premiership after back-to-back defeats to Manchester City and Chelsea at the start of the season.More news: The American Music Awards 2018
However, they have shipped 10 goals already this season and look extremely vulnerable in defence, with summer signing Sokratis and Shkodran Mustafi playing as first choice centre-backs.
The former midfielder has been harsh in his assessment of the team's ability and firmly believes they are due a thrashing.
'Sooner or later they will be on the end of a big score - defensively they are all over the place, ' Merson told Sky Sports.More news: Kavanaugh to hear first arguments as Supreme Court justice
The Gabon global stated that the positive mentality of the team is what gets them going and he is positive the momentum can be maintained for a longer period.
'But defensively, they are just not good enough'.More news: Liverpool's Jurgen Klopp: Nations League a 'senseless' competition
Both stars became the first two substitutes in the Premier League to score and assist a goal in a single game. Based on conversations with his support staff and a study of the player data available to him, Emery believed that Arsenal would be better served training at the Baku Olympic Stadium in Azerbaijan the day before the game rather than doing so at London Colney as they would have done in previous years.