The Manchester United midfielder is being linked with the Belgian giants.
Riemer said, "I know Christian from my time at Brentford, where we worked together. He is a fantastic player. We are in regular communication with each other, but we have been for the last few years.
"I know he is at a training camp in Los Angeles with Manchester United. So I can confirm he is not in Brussels!
"In general, I can say that Jesper Fredberg and our scouts work day and night to get reinforcements, but it's not like you can just take a player off the shelf, as if he were a product in Carrefour (Belgian supermarket).
"It takes time to massage certain targets. At the end of the window, sometimes an opportunity comes, as we saw it last season with Thorgan Hazard."