Manning has impressed since joining the Millers on a season-long loan but Rangers have the option to take him back to Loftus Road when the transfer window reopens.
Rangers allowed the Irishman to go because he was behind the likes of Jordan Cousins, Josh Scowen and Massimo Luongo in manager Steve McClaren’s pecking order of midfielders.
“Every season-long loan has a recall option,” Warne said. “That is obviously my fear.
“It has never been an option that we would buy him, that’s never been a conversation.
“In fairness to Ryan, they think the world of him at QPR. It’s not like they want him out and they want to get rid of him. They actually do like him and want him to play games.
“If he is playing really well and they are struggling in midfield they might have him back or they might do it for another reason.
“It’s a long way to go between now and then.”
Are QPR likely to recall Manning?
QPR officials believe there is a fair chance Manning will be recalled in January – but only if he is likely to play regularly.
Manning is enjoying his time at Rotherham and is likely to seek reassurances that he is in Rangers’ first-team plans should they indicate they want him back at Loftus Road.
He would be reluctant to return in order to sit on the bench – and Rangers are reluctant to recall him against his will.
Much will also obviously depend on the fitness and form of QPR’s other midfielders, particularly Jordan Cousins.
Manager Steve McClaren’s decision to give Cousins more game time was a major factor in Manning being allowed to go.