Willock's contract with the Gunners was set to expire on July 1 and the 19-year-old has rejected an extension to remain with the club in favour of moving to the Portuguese giants.
The England youth international, who has been with the Gunners since the age of five, was one of the most highly-rated players in Arsenal's academy set up and Gunners boss Arsene Wenger revealed towards the end of last season that he had high hopes for the starlet who signed his first professional contract with the club in February 2015.
Chris Willock has signed a five-year deal with Benfica after rejecting a contract extension at Arsenal. Announcement expected shortly. pic.twitter.com/7fa1kSo2cu— Chris Wheatley (@ChrisWheatley_) June 30, 2017
“Chris is a very gifted player with natural strength and natural talent,” Wenger told the Arsenal's matchday programme. “He has what you do not find very easily.
“Overall I would be very comfortable to play him now but of course there is a lot of competition for places because there are players like Walcott, Alexis and Welbeck in front of him at the moment.
“If I had to play him then I would have no fear in doing so. Next season I think he will be a player who will get to feature in the team.”
A skilful winger who has previously played in central midfield, WIllock has regularly trained with the Arsenal first team and was named on the bench for the FA Cup win away to Hull City last season, but the likes of Reiss Nelson and Ainsley Maitland-Niles are both currently considered above him in the pecking order to the senior squad.
Willock's younger brother Joe is currently part of the Arsenal academy set-up and older brother Matty joined Manchester United in 2012.