George Porter is making the step up to the Championship after agreeing a three-year deal with Burnley.
The 20-year-old turned down an improved contract with Orient and has now penned a deal to link up with the Clarets.
Porter arrived at Brisbane Road as Russell Slade’s first signing in the summer of 2010 when the club brought him into the professional game from Ryman Premier Division side Cray Wanderers.
He spent much of his first season on loan in the non-league ranks but appeared 38 times for the club last season, scoring two goals in the process.
The O’s will be entitled to compensation however having offered Porter a new contract. Discussions are ongoing between the two clubs.