Ryan joined Rovers, from Stoke City, in January 2013 in a two and a half year deal and made his debut in a 3-1 win at Rotherham on 26th of that month.
He opened his Rovers account on his home debut, scoring a late winner against Barnet on 1st February 2013 and went on to score five goals in 18 league appearances before the end of the season.
Injury restricted his appearances to 14 in all competitions last season and he trained hard over the summer months in order to be fit again for the current season.
However he has found it difficult to break into the side and has made just four appearances to date.
Manager Darrell Clarke, commenting on Ryan's loan move, said; "Ryan has been to see me on a couple of occasions regarding the possibility of going out on loan and at our last meeting we agreed that it would be beneficial for him.
"I am unable to offer him regular football here at the moment, something he will get with York, and the move gives him the opportunity of playing at a good level and regaining his match sharpness."