Glendon trained with Rangers this week but, despite impressing Warburton, the Light Blues will not be following up their interest by submitting a bid for the youngster.
Warburton also confirmed that his side’s move for Eustace had hit a stumbling block, but they could return to sign the former Derby County man later in the season.
“John's had a domestic situation to deal with at home unfortunately and he's dealing with that now," Warburton said.
"He needs time to deal with it. The club wish him well in that situation and we'll see where we are in a couple of weeks' time.
"We'll do nothing further with George, he's gone back to Man City.
"He's a good technical player and a good all-round guy as well, but he's gone back to his club."
Eustace’s arrival at Rangers would add further quality to their squad, but Warburton will be cautious over bringing in too many new faces.
The Light Blues have made a brilliant start to the new campaign, and they will not want to disrupt their current side’s momentum.
Rangers have established a five point lead at the top of the Scottish Championship, and they have played some brilliant football during that time.
Warburton’s side have won 12 of their first 13 league matches, and they won 4-0 against Alloa Athletic in their most recent outing, which suggests that they won’t need to much extra-quality to be promoted this season.