Schalke 04\'s ex-Germany defender Christoph Metzelder has injured his groin on his first competitive start of the season and will miss Saturday\'s Bundesliga clash against Hoffenheim. The 31-year-old had to come off at half-time in Schalke\'s 3-0 home win over second division SV Sandhausen in the second round of the DFB-Pokal yesterday and it is unclear how long he will be out for. \"I\'m afraid I have a torn muscle in the groin area,\" Metzelder told Schalke\'s website. Schalke host Arsenal in the UEFA Champions League next Tuesday and Metzelder, who won the last of his 47 caps for Germany in the UEFA EURO 2008 final defeat to Spain, faces a race against time to be considered for selection. Since joining Schalke from Real Madrid in July 2010, Metzelder has made 48 league appearances for Die Königsblauen, scoring two goals. From FIFA