Germany reserve goalkeeper Marc-André ter Stegen has a stomach illness and did not fly with the rest of the World Cup squad to their training base in Oman on Monday, the German Football Federation announced. The Barcelona stopper arrived at a Frankfurt hotel late on Sunday along with the rest of the 26-man squad. But it has been decided he will stay in Germany until he is well enough to travel. The players were dressed in smart black suits as they posed for a farewell photograph with coach Hansi Flick before their slightly delayed flight took off for Oman. The plane was adorned with the slogan…