Grayson signed Cardiff's Northern Ireland defender Tony Capaldi, 28, on loan until January 4 and he goes straight into the squad for Sunday's cup tie at Kettering.
It was one of three temporary signings, with QPR winger Hogan Ephraim, 21, joining on loan until Friday, January 1, and Liverpool goalkeeper David Martin, 23, signing until December 28.
Neither Ephraim nor Martin will be allowed to play in the cup tie.
Defender Alan Sheehan, who recently returned to Elland Road from being on loan at Oldham, has joined Swindon on loan until January 4, while striker Davide Somma has moved to Chesterfield until January 2.
Academy product Andrew Milne has also been loaned out to Darlington for the same period.