Cassidy, 23, joined Guiseley in early October and has since made 16 appearances scoring five goals.
The Welshman started his career as a 16 year-old with Llandudno Junction and made a great impression netting 28 goals in 32 games in the 2009-10 season.
This brought him to the notice of a number of clubs and earned him a move to Airbus UK Broughton.
However, his stay there was very short as he impressed in pre-season games and immediately moved on to Wolverhampton Wanderers.
The Premier League side gave him a two year deal.
He had loan spells at Tranmere Rovers, Notts County and Southend before signing for Oldham Athletic in 2015.
Cassidy is the partner of teammate Simon Walton's sister Sophie, herself a former player with Leeds United, Notts County and England.