Gagen, 19, joins the BetVictor N/West Division team on a youth loan until the end of the current season.
The defender joined Barnsley in October 2015 and signed his first scholarship with the Reds in July 2017.
A versatile defender, he is capable of playing anywhere across the back four but is more natural in the full-back position where he is able to bomb forward and support the attacks.
Keep up-to-date with our exclusive email newsletters.
Subscribe