Andrei Arshavin believes Arsenal's results against their rivals this season show that the current squad is not equipped to compete for silverware.
Arsenal have enjoyed some impressive form so far this season, but they were beaten by Manchester United and Manchester City in the league in August and September and lost to Sunderland and Chelsea in November.
Many have suggested that the 3-0 defeat at home to Chelsea on Sunday showed that Arsene Wenger will need to invest in January if Arsenal are to remain in the title race and Arshavin believes the lack of height and physical strength must be rectified as soon as possible.
"The fact that we have lost against our direct rivals this season signifies that we are not very good," he said in the Daily Mail. "We played good football, but that is not enough. We score a lot of goals, but we always let in one or more.
"We are not good on set pieces, and that is bound up with the fact that we don't have many tall players. Every other team as an advantage over us in this area. Chelsea were much stronger than us when it came to physical power.
"Had we possessed a tall player, things would have been better for us, especially in attack. We had nobody capable of holding up the ball. What can we, and must we, change? Only Arsene Wenger knows."
Wenger has indicated that he hopes to sign a striker in January following the injury to Robin van Persie.