The former Millwall and Southampton wide man has recently been given an extension to his initial short-term deal until January.
Smith has made just four substitute appearances since arriving in August and Warnock has told him he must improve his form if he is to become a regular.
"He's got to become more consistent and start creating things in the final third," Warnock told the Croydon Advertiser.
"This deal gives him a few more months to put forward his case."
Source: Team_Talk