Despite signing two defenders over the summer, with Chelsea's David Luiz starting against Tottenham, Unai Emery's backline continues to struggle having conceded 51 goals last season - more than top two Manchester City and Liverpool let in combined.
Former Newcastle striker Shearer declared the Gunners' defence has only gotten worse over the off-season and that it will be a major issue for the club.
"Arsenal's defending was comical at times in the first half – it was Sunday League stuff," Shearer wrote in The Sun.
"From start to finish, it was embarrassing how easy it was for Tottenham to get their two first-half goals.
"If anything, Arsenal are worse now than they were last season. Kieran Tierney is yet to come in but on this evidence they certainly haven’t improved defensively. I see that as being an issue for Arsenal again going forward – a big problem."
Despite taking advantage of the Gunners' defensive frailties in the first-half, Spurs would surrender their 2-0 lead in the second 45 minutes at the Emirates as their winless run extended to three matches.
Shearer of the belief that both Tottenham and Arsenal will be forced to really battle it out for a spot in the top four with the title race already down to two teams.
"They (Spurs) look very reliant on Kane’s goals but I still think they will be fighting for a place in the top four," Shearer wrote.
"In Eriksen they had someone who could put their foot on the ball and Spurs boss Mauricio Pochettino will be delighted that the European transfer window is coming to an end.
"Spurs and Arsenal will be among four sides fighting for Champions League places who all have issues.
"Manchester City and Liverpool are a million miles ahead of the rest."
As it stands, Arsenal sit fifth and Tottenham ninth in the Premier League with Liverpool top of the table, five points clear of the Gunners and seven ahead of Spurs after just four games.