22-year-old Roberts, who missed the whole of last season after suffering a broken leg during a pre-season clash with Stoke City, has only featured four times so far this season, with his most recent outing coming off the bench against Crawley Town in mid January.
The Birmingham-born centre-back has started only one game so far this season - as the Saddlers suffered a 2-1 defeat to Mansfield Town in late October - and Clarke insists he is clear on what he wants to see from Kory.
Speaking via the Express & Star, Darrell said; "Do a lot better in the reserves. I like Kory as a lad, I’ve had a good conversation with him and he knows where I stand on things.
"Kory is a good lad but he needs to raise his standards that I set and he’s working hard to do that. You’ve got to prove it to me and to my staff on a consistent basis and Kory’s got to do that to try and earn himself a new deal in the summer."