The Republic of Ireland Under 21 international keeper trained with Brian Tinnion's first team squad this week.
Discussions are now underway between the two clubs to see if Henderson can play in a behind-closed-doors practice match for City this week
"I wouldn't want to sign him unless I can have a look at him in a match," Tinnion told the clubs official website.
"Wayne has gone back to Aston Villa and we will continue discussions with them. But at this stage it is unlikely anything will happen on that one."