Gardner was most recently on loan at Brighton and Hove Albion - where he scored two goals in 11 games - and joins Chelsea full back Todd Kane at the City ground after he was signed on loan on Thursday [January 8].
22-year-old Gardner's wages will be paid by the Sky Bet Transfer Fund.
Fan Shaun Lander was selected at random from over 70,000 fans in a draw at Wembley on December 16.
Landscape gardener Shaun, who also won £5,000 for himself, said: "As a Nottingham Forest fan I'm delighted that the club has been able to add a second player to the squad using the Sky Bet Transfer Fund.
"Hopefully both Todd and Gary can make the difference for Stuart between now and the end of the season."