He has scored just four goals over the course of a difficult first 12 months, while a number of niggling injuries have hindered his progress.

He is back in contention to feature against his former club in the FA Cup fourth round after overcoming a hamstring issue and it could be his first appearance at Arsenal since his departure, with head coach Emery revealing he had been keen on landing Sanchez when manager of PSG.

Asked if he tried to sign the former Barcelona forward, the Spaniard replied: "Yes. He is a very good player and, when I was at PSG, we thought he could help him.

"We spoke about a lot of players, about a lot of important players, and one was the possibility of Alexis. But it was not possible."

Instead Sanchez moved north to join United, who have won all seven of their games under interim manager Ole Gunnar Solskjaer.

Former boss Jose Mourinho was sacked in December, with a 2-2 Premier League draw with Arsenal one of his final games at the helm.

Sanchez was injured for that match, but, despite his troubles, Emery knows his defence have to be aware that the 30-year-old can be a threat.

"I respect him," Emery added.

"In my preparations, every player is (prepared in) playing against the best players from Manchester United and one is Alexis Sanchez.

"I don't know why his performances or quality is better or worse in these circumstances. Now, in the last matches, they are playing very, very well with very big performances.

"He's been starting on the bench after an injury, but, if he plays Friday, we need to work to stop him because he is a very good player."

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