If there is one Chelsea player who can be satisfied with his performances so far this season, it’s Willian.

The Brazilian has emerged as a key player while the likes of Eden Hazard, Diego Costa and Cesc Fàbregas have struggled for form in a dismal season for last year’s champions. But Willian has, if anything, gone up a level.

In a struggling Chelsea side which hasn’t managed to create much since August, only Diego Costa has scored more than Willian’s three Premier League goals. No Chelsea player has assisted more often than the winger in the Premier League, and in the Champions League the Brazilian netted five goals in six games. Through the entire group stage the rest of the Chelsea squad managed six goals between them.

Arsenal's Spanish defender Nacho Monreal (R) vies with Chelsea's Brazilian midfielder Willian during the FA Community Shield football match between Arsenal and Chelsea at Wembley Stadium in north London on August 2, 2015. AFP PHOTO / IAN KINGTON -- NOT FOR MARKETING OR ADVERTISING USE / RESTRICTED TO EDITORIAL USE -- (Photo credit should read IAN KINGTON/AFP/Getty Images)
Willian v Nacho Monreal. This will be a key battle on Sunday as Arsenal welcome Chelsea to the Emirates Stadium. (IAN KINGTON/AFP/Getty Images)

While they have a number of quality players, Willian is the one Arsenal must look out for most this weekend.

“He is very tricky, very good at dribbling and at getting past people,” Arsène Wenger admitted to Arsenal.com“He is a very mobile player and also very hard-working.

“He combines so many qualities and the fact he is not very tall but very agile and quick to change his direction makes him difficult to read for his opponents.”

On the right wing, Willian will be up against Nacho Monreal. If Mesut Özil and Petr Čech weren’t so good at what they do, Monreal would be considered one of the best and certainly the most consistent player in the Arsenal squad. He’s integral and will be tasked to stop Willian on Sunday.

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The Spaniard is more than capable but, as Wenger rightly seems to think, stopping Willian will be key to Arsenal’s chances.