The France international missed training on Thursday morning, before Dortmund then announced that Barcelona had made a bid for the forward.
Barcelona's approach was rejected by the German giants but that has not put off the Spanish giants just yet.
Reports suggest they are planning to return with a bigger offer as they look for a replacement for Neymar who joined Paris Saint-Germain.
He has yet to return to training and is refusing to discuss his actions with the club and the former Rennes star is set to miss Saturday's DFB Cup tie against FC Rielasingen-Arlen.
Dortmund chiefs will be hoping to resolve the issue before their first league game against Wolfsburg as they continue to insist he will not be sold.