Neither Benfica nor Arsenal have confirmed the move, but the 19-year-old has been pictured in the Portuguese club's strip at their ground, suggesting that all of the official paperwork has been signed.
Willock, whose brother Matty Willock currently represents Manchester United, trained with Arsenal's first team last season, and was named on the bench for the FA Cup clash with Hull City, in addition to making two appearances in the League Cup.
The England youth international has seemingly turned down the chance to pen an extension with the Gunners, however, as he looks to make the grade with Benfica.
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
Forward Willock has scored twice in seven appearances for England's Under-19 team.