I'm not sure I can see us signing a back up RB. Not unless they are a young RB.
If Ron sees Cedric as being good enough to be a first choice RB, then there is no desperate need to sign a back up. We didn't last year for Clyne, and we didn't really this summer for Cedric.
But the fact that he isn't featuring anywhere near as regularly as Clyne (and remembering the lack of back up) suggests to me that, at least at present, Ron doesn't see Cedric like that. He's our Chambers to our non-existent Clyne, if you like. So if we are to sign a RB, then I'm going for first choice RB - or at the very least, another young RB who can develop. And you don't get those in January, generally*.
*Note the lack of the word "but" or "unfortunately" etc. Personally, I think Cedric is fine. I really like him. Yes he was very poor against Stoke, but everyone has a poor game at some point (though not Virgil yet!)