The 20-year-old, who can play either at left-back or winger, was formerly with Brighton and Hove Albion, progressing from the Sussex's club academy to professional.
He spent three months on loan with Dover Athletic - managed by ex-Bee Nicky Forster - last season before being released this summer.
Leon has played in all in the club’s first team pre-season schedule so far and is expected to feature in Saturday’s game at Basingstoke Town.
He will be added to the development squad for this season, whose next game is at Stoke City on Thursday, August 9.
Ose Aibangee, Brentford’s Head of Youth Development, said: “Leon will supplement the development squad and group but ultimately his - and our aim is for him to get into the first team”.
You can view an exclusive Bees World interview with Leon via the link below: