Routledge has been in impressive form this season, helping Rangers to the top of the Championship table with four goals and five assists.
The winger's agent recently indicated he would return to St James' Park at the end of the season.
But Warnock told BBC Sport: "I really don't see any problems, to be honest.
"It's up to us now to dot the Is and cross the Ts. I think he's set his mind on coming here now, and we want him."
Source: PA
Source: PA