Mohamed Zidan is doubtful for Borussia Dortmund's Bundesliga game at Karlsruhe on Friday, the German club said. Dortmund said on their website that the Egyptian forward might not be able to take part in the match due to a stomach injury. Should Zidan fail to recover in time for the match, Dortmund manager Jurgen Klopp will face selection dilemma. Striking duo Diego Klimowicz and Nelson Valdez are also doubtful due to injury and illness respectively. Zidan has struggled to make an impact since joining from Hamburg SV in the close season. Having been blighted by persistent injury problems, the 26-year-old scored just two goals in the Bundesliga so far.