Arsenal great Robert Pires believes the Premier League title race will be over if his former club lose to runaway leaders Chelsea on Saturday.
Arsene Wenger's side went down to a shock 2-1 defeat at home to Watford on Tuesday, meaning Chelsea's 1-1 draw at Liverpool left Antonio Conte's men nine points clear at the summit.
Chelsea have been in formidable form since Conte switched to a 3-4-2-1 system on the back of a chastening 3-0 loss at Emirates Stadium in September.
And Pires acknowledges the Gunners have little margin for error with 15 top-fight games remaining this term.
"It will be very difficult after the last game that we lost against Watford. It was terrible," the ex-Gunners star told reporters.
"We have another chance next Saturday. For me this is a big final for the Premier League. If Chelsea beat Arsenal I think the Premier League is done.
"Chelsea play very well, they are a very good team, very compact. They have the Italian philosophy, they play together.
"Chelsea are maybe stronger but we need to believe in this opportunity. I think this is the last opportunity."
Pires' compatriot and former Chelsea defender Marcel Desailly believes the Blues possess a more robust playing unit and predicts this could be the difference.
"Arsenal is having a problem because they have possession of the ball all the time but they don't make the difference," he 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."