Saturday the Gunners will travel to Stamford Bridge, nine points behind their hosts, after they lost 2-1 to Watford at the Emirates on Tuesday.
Arsenal crushed Chelsea 3-0 in the reverse fixture last September, but their title hopes are faded away slightly, while Antonio Conte's men marched on.
“Arsenal is having a problem because they have possession of the ball all the time but they don't make the difference,” Desailly said.
“When you are facing Chelsea you are have a problem because Chelsea has this capacity to really control the game, handle the pressure the opponent will put on them and have a great transition from defence to make the difference up front with Diego Costa.
“Arsenal need a [Nemanja] Matic or N'Golo Kante. You can see that the protection of their defensive block is not enough.
“You have the ability to play, the ability to use the ball but the defensive protection is not at the level you would expect because all the players have pretentions on playing.”
Desailly added: “If you lose against Watford it is difficult to get the state of mind for winning to straight away compete against Chelsea.
“For Chelsea it is not crucial, you prepare for the game normally. Yes, it's an important game, a derby but it is not something crucial for Chelsea, winning and losing.
“The important thing is to have consistency throughout the rest of the season. Then you are sure to win the league in that case.”